Traditional Chinese Medicine Herbs for Breast Cancer Prevention and Survival: A Narrative Review of Epidemiological Studies from Taiwan.

A total of 448 papers were screened, revealing 262 duplicates ( Figure 1 – Consort Diagram). A supplementary manual search in Google Scholar uncovered 4 additional papers meeting the inclusion criteria. After assessing each paper for exclusion criteria 7 papers remained, all published from 2011 to 2023 in peer-reviewed journals. ( Table 1 ) All 7 studies included only women, with ages ranging from 18 to 89. The sample size varied from 729 to 184,386. Covariates included age, geographic area, urbanization, income, conventional medical (CM) treatments (including pharmaceutical drugs), comorbidities/Charlson Comorbidity Index (CCI) Score, and Hospital type (Private vs Public). Four observational studies assessed the risk of developing breast cancer in women with vs. without exposure to TCM herbal products. ( Table 1a ) These included 2 cohort studies[ 34 , 35 ] and 2 matched case-control studies[ 36 , 37 ]. All 4 focused on women with comorbid conditions: menopausal symptoms[ 34 ], diabetic mellitus type II[ 36 ], and one or more history of other medical conditions.[ 35 , 37 ] Three observational cohort studies examined breast cancer mortality/survival in women with vs. without exposure to TCM herbs. ( Table 1b ) Two[ 38 , 39 ] included patients newly diagnosed with breast cancer while one[ 40 ] investigated patients with only estrogen receptor positive breast cancer. All 4 studies assessing the risk of developing breast cancer reported benefits to TCM herbal use: In an observational cohort study of 17,583 menopausal women ages 55–79 with exposure to exogenous hormone therapy (eHT; estrogen-alone, and mixed type), authors evaluated the association between exposure to eHT plus TCM herbal products and risk of breast cancer development from 1997 to 2008.[ 34 ] eHT users were stratified by current users and recency of use (eHT last used 1–3, 4–5, ≥6 years ago). The authors reported hazard ratios (HR), and 95% confidence intervals (CI) for breast cancer risk estimated using the univariate Cox regression model. Among women exposed to Estrogen alone with vs without herbal products, HR were 0.30 (0.05–1.81), 1.21 (0.08–19.41) and 0.90 (0.08–9.91), for current users, last used 4–5 and ≥6 years ago, respectively. Among women exposed to mixed type eHT with vs without herbal products, HR were 0.39 (0.13–1.24), 2.87 (0.36–22.98), and 0.53 (0.25–1.15), for current users, last used 1–3, and ≥6 years ago, respectively. ( Table 2 ) The same research group expanded the age groups to 20–79 years of age and followed 184,386 women from 1999 to 2012.[ 35 ] In this observational cohort study, they evaluated the association between exposure to TCM herbs and a subgroup of patients taking a specific herbal formula, Si Wu Tang (SWT; containing Shu Di Huang (Rehmanniae Radix Preparata), Dang Gui Angelicae Sinensis Radix), Bai Shao (Paeoniae Alba Radix), and Chuang Xiong (Chuanxiong Rhizoma) known to contain phytoestrogen)[ 41 , 42 ] vs TCM herbnon-users and risk of breast cancer. The authors reported covariate adjusted hazards ratios (95% CI) for breast cancer were 0.57 (0.50–0.65) and 0.36 (0.28–0.46) in women using TCM herbs and SWT, respectively (adjusted for age, geographic area, urbanization status, history of diabetes, obesity, oophorectomy, endometriosis, myoma, irregular menstrual, premenstrual syndrome, polycystic ovary syndrome, abortion, and eHT usage). Authors concluded that TCM herbs and SWT were associated with lower risk of developing breast cancer, although the mechanism of action is not clear. ( Table 2 ) The same research team examined 33,828 women with type 2 diabetes mellites (DM-II) taking metformin and other anti-diabetic drugs ages 20–79 years during 2001–2012 in a 1:10 matched case-control observational study.[ 36 ] Authors evaluated the association between the exposure to TCM herbs ± Di Huang Wan Series (DHWS; containing Di Huang (Rehmanniae Radix) as one of the main ingredients) and breast cancer development. The DM-II patients were stratified into TCM herbal use 500 grams use excluding DHWS, and > 500 grams use including DHWS. The adjusted hazard ratios (aHR; 95% CI) for breast cancer estimated using the multivariate Cox regression model (adjusted for metformin and other antidiabetic drugs used, and hormone therapy used) in women with DM-II ages 20–79. The aHR were 1 (reference), 0.57 (0.45–0.73), and 0.45 (0.34–0.59), for TCM herbal use 500 g excluding DHWS and > 500 g including DHWS, respectively. The authors concluded that there was an observed protective effect of TCM herbal use whether it included DHWS or not. ( Table 2 ) In a matched case-control observational study, a separate research group analyzed 137,048 women (case-control 1:3 ratio) from 2005–2008.[ 37 ] The authors explored the association between the exposure to Angelica sinensis Radix (AS; also known as Dang Gui) by different dosages and by different ages of initial AS use and breast cancer diagnosis risk. The overall adjusted odds ratios (aOR) (95% CI p-value); adjusted for residential area, monthly salary, gynecology cancer, benign breast/uterine tumor, metabolic disease, and estrogen/progesterone exposure) of breast cancer in association with AS exposure was 0.95 (0.93–0.98) p<0.0001. The aORs (95% CI p-values) by weight of AS were 0.97 (0.93–1.00) P<0.06, 0.93 (0.89–0.97) p<0.001, and 0.96 (0.91–1.00) p<0.06 for 0.1–9.9 grams, 10–29.9 grams, and ≥ 30 grams exposure, respectively (p for trend <0.001). The aORs (adjusted for age, residential area, monthly salary, gynecology cancer, benign breast/uterine tumor, metabolic disease, and estrogen/progesterone exposure) of breast cancer in association with initial use of AS were examined relative to menopausal status. The authors concluded that AS was associated with a weakly but significantly reduced risk of breast cancer, which contradicted concern that as a phytoestrogen it may increase breast cancer risk. ( Table 2 ) In an observational cohort study of 17,583 menopausal women ages 55–79 with exposure to exogenous hormone therapy (eHT; estrogen-alone, and mixed type), authors evaluated the association between exposure to eHT plus TCM herbal products and risk of breast cancer development from 1997 to 2008.[ 34 ] eHT users were stratified by current users and recency of use (eHT last used 1–3, 4–5, ≥6 years ago). The authors reported hazard ratios (HR), and 95% confidence intervals (CI) for breast cancer risk estimated using the univariate Cox regression model. Among women exposed to Estrogen alone with vs without herbal products, HR were 0.30 (0.05–1.81), 1.21 (0.08–19.41) and 0.90 (0.08–9.91), for current users, last used 4–5 and ≥6 years ago, respectively. Among women exposed to mixed type eHT with vs without herbal products, HR were 0.39 (0.13–1.24), 2.87 (0.36–22.98), and 0.53 (0.25–1.15), for current users, last used 1–3, and ≥6 years ago, respectively. ( Table 2 ) The same research group expanded the age groups to 20–79 years of age and followed 184,386 women from 1999 to 2012.[ 35 ] In this observational cohort study, they evaluated the association between exposure to TCM herbs and a subgroup of patients taking a specific herbal formula, Si Wu Tang (SWT; containing Shu Di Huang (Rehmanniae Radix Preparata), Dang Gui Angelicae Sinensis Radix), Bai Shao (Paeoniae Alba Radix), and Chuang Xiong (Chuanxiong Rhizoma) known to contain phytoestrogen)[ 41 , 42 ] vs TCM herbnon-users and risk of breast cancer. The authors reported covariate adjusted hazards ratios (95% CI) for breast cancer were 0.57 (0.50–0.65) and 0.36 (0.28–0.46) in women using TCM herbs and SWT, respectively (adjusted for age, geographic area, urbanization status, history of diabetes, obesity, oophorectomy, endometriosis, myoma, irregular menstrual, premenstrual syndrome, polycystic ovary syndrome, abortion, and eHT usage). Authors concluded that TCM herbs and SWT were associated with lower risk of developing breast cancer, although the mechanism of action is not clear. ( Table 2 ) The same research team examined 33,828 women with type 2 diabetes mellites (DM-II) taking metformin and other anti-diabetic drugs ages 20–79 years during 2001–2012 in a 1:10 matched case-control observational study.[ 36 ] Authors evaluated the association between the exposure to TCM herbs ± Di Huang Wan Series (DHWS; containing Di Huang (Rehmanniae Radix) as one of the main ingredients) and breast cancer development. The DM-II patients were stratified into TCM herbal use 500 grams use excluding DHWS, and > 500 grams use including DHWS. The adjusted hazard ratios (aHR; 95% CI) for breast cancer estimated using the multivariate Cox regression model (adjusted for metformin and other antidiabetic drugs used, and hormone therapy used) in women with DM-II ages 20–79. The aHR were 1 (reference), 0.57 (0.45–0.73), and 0.45 (0.34–0.59), for TCM herbal use 500 g excluding DHWS and > 500 g including DHWS, respectively. The authors concluded that there was an observed protective effect of TCM herbal use whether it included DHWS or not. ( Table 2 ) In a matched case-control observational study, a separate research group analyzed 137,048 women (case-control 1:3 ratio) from 2005–2008.[ 37 ] The authors explored the association between the exposure to Angelica sinensis Radix (AS; also known as Dang Gui) by different dosages and by different ages of initial AS use and breast cancer diagnosis risk. The overall adjusted odds ratios (aOR) (95% CI p-value); adjusted for residential area, monthly salary, gynecology cancer, benign breast/uterine tumor, metabolic disease, and estrogen/progesterone exposure) of breast cancer in association with AS exposure was 0.95 (0.93–0.98) p<0.0001. The aORs (95% CI p-values) by weight of AS were 0.97 (0.93–1.00) P<0.06, 0.93 (0.89–0.97) p<0.001, and 0.96 (0.91–1.00) p<0.06 for 0.1–9.9 grams, 10–29.9 grams, and ≥ 30 grams exposure, respectively (p for trend <0.001). The aORs (adjusted for age, residential area, monthly salary, gynecology cancer, benign breast/uterine tumor, metabolic disease, and estrogen/progesterone exposure) of breast cancer in association with initial use of AS were examined relative to menopausal status. The authors concluded that AS was associated with a weakly but significantly reduced risk of breast cancer, which contradicted concern that as a phytoestrogen it may increase breast cancer risk. ( Table 2 ) All 3 studies assessing breast cancer mortality reported benefits to TCM herbal use: An observational cohort study, investigating a 10-year follow-up period on 729 female patients receiving taxanes (docetaxel or paclitaxel), which were determined by Bureau of National Health Insurance to be reimbursable only for patients with locally advanced or metastatic breast cancer.[ 38 ] Study authors evaluated the association between TCM users (patients using TCM for > 30 days) vs TCM non-users (non-users, or treated with TCM < 30 days) and mortality, further evaluating dose-response (TCM used for 180 days). In an overall adjusted Cox proportional hazards model, TCM use was found to be associated with significantly decreased risk of all-cause mortality. When examined by dose response, persons using TCM for 180 days, respectively. The authors concluded that adjunctive TCM therapy is associated with lower risk of death in patients with advanced breast cancer. ( Table 2 ) An observational cohort study that explored the relationship between TCM exposure and overall survival in a study of 872 patients with any stages of estrogen receptor positive breast cancer, ages 20–89 years receiving adjuvant hormone therapy (aHT; such as tamoxifen, anstrozole, letrozole, and exemestane) within first year after primary BC surgical intervention, where each patient was followed up 5 years.[ 40 ] The authors evaluated the association between TCM exposures vs TCM non-exposure, and mortality rate. The hazard ratios (95% CI p-value) for mortality among patients who visited traditional Chinese medicine practitioners at least 3 times a year, and who were prescribed TCM herbs with duration of 1–90 days per year was 0.26 (0.08–0.83) p=0.0227. The authors concluded the potential advantage of adjuvant TCM herbal therapy on breast cancer-associated mortality. ( Table 2 ) An observational cohort study following 5387 patients with breast cancer over age of 18 from 2000 to 2010.[ 39 ] The authors evaluated the association between exposure to San-Huang-Xie-Xin-Tang (SHXXT; containing Da-Huang [Rhei Radix et Rhizoma], Huang-Lian [Coptidis Rhizoma] and Huang-Qin [Scutellariae Baicalensis Radix]) and mortality, by treatment modality, adjusting for age, urbanization level, CCI score, conventional treatments, and pharmaceutical drugs. The adjusted HR (95% CI p-value) for SHXXT and mortality was 0.43 (0.38–0.49) among women receiving surgery; among women receiving radiotherapy was 0.46 (0.41–0.53); and for chemotherapy, it was 0.45 (0.4–0.5). The association was examined by duration of SHXXT use vs non-SHXXT users among patients with breast cancer were 0.44 (0.38–0.50) p < 0.001, 0.41 (0.33–0.50) p < 0.001, and 0.31 (0.24–0.40) p 180 days, respectively (p for trend <0.001). Associations were then examined by annual average SHXXT dose vs non-SHXXT users (as reference), with effect estimates of 0.50 (0.42–0.60), 0.43 (0.35–0.51), 0.39 (0.32–0.48), and 0.30 (0.24–0.38) observed for 147 g/year, respectively (p for trend <0.001). The authors concluded that SHXXT and its constituents were promising therapeutic weapons against breast cancer. ( Table 2 ) An observational cohort study, investigating a 10-year follow-up period on 729 female patients receiving taxanes (docetaxel or paclitaxel), which were determined by Bureau of National Health Insurance to be reimbursable only for patients with locally advanced or metastatic breast cancer.[ 38 ] Study authors evaluated the association between TCM users (patients using TCM for > 30 days) vs TCM non-users (non-users, or treated with TCM < 30 days) and mortality, further evaluating dose-response (TCM used for 180 days). In an overall adjusted Cox proportional hazards model, TCM use was found to be associated with significantly decreased risk of all-cause mortality. When examined by dose response, persons using TCM for 180 days, respectively. The authors concluded that adjunctive TCM therapy is associated with lower risk of death in patients with advanced breast cancer. ( Table 2 ) An observational cohort study that explored the relationship between TCM exposure and overall survival in a study of 872 patients with any stages of estrogen receptor positive breast cancer, ages 20–89 years receiving adjuvant hormone therapy (aHT; such as tamoxifen, anstrozole, letrozole, and exemestane) within first year after primary BC surgical intervention, where each patient was followed up 5 years.[ 40 ] The authors evaluated the association between TCM exposures vs TCM non-exposure, and mortality rate. The hazard ratios (95% CI p-value) for mortality among patients who visited traditional Chinese medicine practitioners at least 3 times a year, and who were prescribed TCM herbs with duration of 1–90 days per year was 0.26 (0.08–0.83) p=0.0227. The authors concluded the potential advantage of adjuvant TCM herbal therapy on breast cancer-associated mortality. ( Table 2 ) An observational cohort study following 5387 patients with breast cancer over age of 18 from 2000 to 2010.[ 39 ] The authors evaluated the association between exposure to San-Huang-Xie-Xin-Tang (SHXXT; containing Da-Huang [Rhei Radix et Rhizoma], Huang-Lian [Coptidis Rhizoma] and Huang-Qin [Scutellariae Baicalensis Radix]) and mortality, by treatment modality, adjusting for age, urbanization level, CCI score, conventional treatments, and pharmaceutical drugs. The adjusted HR (95% CI p-value) for SHXXT and mortality was 0.43 (0.38–0.49) among women receiving surgery; among women receiving radiotherapy was 0.46 (0.41–0.53); and for chemotherapy, it was 0.45 (0.4–0.5). The association was examined by duration of SHXXT use vs non-SHXXT users among patients with breast cancer were 0.44 (0.38–0.50) p < 0.001, 0.41 (0.33–0.50) p < 0.001, and 0.31 (0.24–0.40) p 180 days, respectively (p for trend <0.001). Associations were then examined by annual average SHXXT dose vs non-SHXXT users (as reference), with effect estimates of 0.50 (0.42–0.60), 0.43 (0.35–0.51), 0.39 (0.32–0.48), and 0.30 (0.24–0.38) observed for 147 g/year, respectively (p for trend <0.001). The authors concluded that SHXXT and its constituents were promising therapeutic weapons against breast cancer. ( Table 2 )

Data from Eastern Asian countries can offer critical insights into safe and effective integration of traditional and conventional modalities.[ 27 ] In these countries, use of herbal supplements and other traditional therapies is integral to longstanding cultural beliefs around maintaining general health and preventing and treating disease. Thus, while modern healthcare in the east has embraced conventional cancer treatment guidelines, it also recognizes the benefits of traditional remedies. Accordingly, eastern patients are commonly prescribed herbs, not only to prevent cancer but also to promote survival. In Taiwan, patients with cancer have enjoyed nearly universal access to both conventional and TCM therapies since 1996. As the single payer, Taiwan’s National Health Insurance (NHI) system issues patients with severe and life-threatening conditions, such as cancer, Catastrophic Illness Certificates (CICs) after thorough evaluations of pathological, laboratory, and clinical findings. Patients who hold CICs for cancer are then entitled to receive both conventional medicine and TCM therapies, free of any copayments or other out-of-pocket expenses. NHI-covered TCM therapies include Chinese herbal preparations, acupuncture, moxibustion (a form of heat therapy), and manipulative therapy (such as deep tissue massage and bone setting). To date, NHI covers 406 TCM multi-herb formulas and over 494 single-herb TCM preparations.[ 28 ] The contents of TCM herbal formulas are developed in accordance with the Department of Chinese Medicine and Pharmacy, Ministry of Health and Welfare, and the quality control requirements by the Taiwan Herbal Pharmacopeia ( https://www.mohw.gov.tw/lp-3690-2.html ). All TCM herbal products are manufactured by Good Manufacturing Practice (GMP)-Certified pharmaceutical companies in granule oral formulations.[ 26 , 29 ] Since 1997, data on all patients with NHI coverage has been available for academic research. The Taiwan National Health Insurance Research Database (NHIRD) provides patient-level information including demographics, health status (including disease diagnoses), conventional medicine (CM)and TCM herbal use, and clinical outcomes, including cancer incidence and mortality.[ 30 ] The NHI administration regularly reviews this database to ensure its accuracy and completeness. To date, over 2,700 peer-reviewed studies using NHIRD data have been published, and these have been instrumental in guiding both clinical decisions and healthcare policy.[ 30 – 33 ] A comprehensive search of epidemiological studies was conducted using PubMed, Scopus and Embase databases, with additional manual searching via Google Scholar. The search strategy employed keywords related to breast cancer prevention or overall survival, TCM herbal use, and the Taiwan National Health Insurance Research Database (NHIRD). Titles and abstracts were screened to exclude duplicates, as well as studies focused on therapies other than TCM herbal use, outcomes other than breast cancer prevention or survival, publications for which no English-language translation was available, and data sources outside of the Taiwan NHIRD. Data from each included study was extracted by 1 reviewer (YNH), with 2 additional reviewers (AY and DR) reviewing the dataset for accuracy. All discrepancies were reviewed by the research team to reach consensus on the final dataset. Extracted data included study period, population (including but not limited to demographics and diagnoses); exposure(s) (including but not limited to CMs, TCM herbal formulas and single herbs, and dosages and duration); and outcomes (e.g., odds of developing breast cancer and hazard ratios of mortality or survival).

While the use of TCM herbal medicine is burgeoning among patients hoping to prevent breast cancer or improve their odds of survival, studies of TCM efficacy are often compromised by inequitable patient access and other methodological limitations. This narrative review surveyed epidemiological studies from Taiwan, where access to both TCM and conventional cancer treatments is universal and rigorously documented in a national database. Findings from this uniquely robust data source suggest TCM herbal use is associated with reduced the risk of developing breast cancer and improved survival, at least in the specific populations studied. However, the relationship is based on observational data. Rigorous clinical trials are urgently needed to further investigate the safe, effective integration of TCM herbs into breast cancer prevention and management.

This narrative review is the first to consolidate evidence from real-world, population-based observational studies on adjunct TCM herbal use for breast cancer prevention and survival. Leveraging peer-reviewed epidemiological studies from Taiwan’s uniquely robust dataset, we found some evidence of protective potential of TCM herbal in the setting of breast cancer prevention. More, there was some evidence to suggest that TCM herbs may prolong survival among certain subgroups of patients with breast cancer receiving conventional treatments.[ 43 ] It must be emphasized that for all the patients with breast cancer included in the NHIRD, it is necessary to receive a precise diagnosis from the breast cancer oncologists or surgeons to hold the CICs with the privilege of no-copayments. TCM herbal products are prescribed as an adjunctive therapy for cancer patients in Taiwan.[ 44 ] Among the studies exploring TCM use and breast cancer prevention, coadministration of exogenous hormonal therapy (eHT) and TCM herbal products was not associated with an increased risk of breast cancer in menopausal women compared to eHT-alone, suggesting a potential preventive effect. Additionally, exposure to the TCM herb Angelica sinensis Radix was found to have a weak but significant protective effect, particularly at higher dosages, showing a dose-response relationship with a P-value for trend <0.001. These findings are consistent with centuries of TCM practice, in which herbal medicines, particularly those containing Angelica sinensis Radix, are often used to address symptoms common in menopausal women such as fatigue, mood issues, and hot flashes.[ 45 ] While some data suggest these herbs have phytoestrogen effects, it is possible that these herbs modulated the dosage/duration of hormonal treatment or acted as partial antagonists to estrogen receptors. More research is needed to rigorously evaluate the efficacy and mechanisms of specific TCM regimens for breast cancer prevention while addressing common symptoms of menopausal transition (e.g. hot flashes, insomnia, anxiety, and joint pain). Among the studies of survival outcomes, TCM use was associated with lower all-cause mortality in locally advanced or metastatic breast cancer patients receiving taxanes and in newly diagnosed patients engaging in annual TCM visits with prescribed TCM herbal medicines. Overall, these findings underscored a potential association between TCM use and enhanced breast-cancer-related survival outcomes, at least in these specific populations. These findings comport with those of a recent Cochrane review[ 43 ]: limited evidence from randomized controlled trials indicates that incorporating TCM herbs alongside chemotherapy may offer benefits such as ameliorating marrow suppression and bolstering the immune system. Similarly, herbs that reduce common toxicities and side effects from breast cancer treatments, such as fatigue and nausea/vomiting, can promote treatment tolerance and adherence and, in turn, survival.[ 16 ] Nevertheless, additional research is needed to rigorously assess the efficacy of TCM herbs for breast cancer patients.[ 46 ] Specifically, large scale, prospective randomized controlled trials are needed to investigate the safety and efficacy of TCM herbs alongside conventional breast cancer treatments. The strength of this review lies in its use of NHIRD data from Taiwan, which provides universal coverage for both conventional and TCM treatments and therefore includes an economically, geographically, and socially diverse sample of cancer patients. As mentioned earlier, the case ascertainment for breast cancer is of high quality due to the payment requirement. Additionally, the NHIRD dataset provides rigorous documentation of TCM use alongside CM treatments, a combination rarely available in other health system datasets. Taiwan’s database also allows for longitudinal tracking of patients and their treatments, providing valuable insights into patterns of TCM herbal use and breast cancer outcomes. The unique strengths of this dataset thus circumvent many major challenges common in observational research on TCM use and breast cancer outcomes: In populations without such comprehensive, universal coverage, variations in patients’ ability to obtain and afford treatments can severely compromise findings. There are also some limitations to consider. First, while the studies included in this review leverage a large, rich database, we should acknowledge the potential for confounding by factors not captured in the NHIRD database, such as body mass index or lifestyle factors that may be associated with both exposure and outcome. However, the studies sought to mitigate confounders by properly matching the cohorts.[ 44 ] Another limitation is possible underestimating TCM use; NHIRD is claims based data, only TCM herbs prescribed by licensed doctors can be reimbursed, not over-the-counter TCM herbs. More, in the studies focused on risk/prevention, no data on breast cancer staging or histological pathology data were included, due to limitations of the NHIRD database. Future studies should incorporate such crucial data could help understand whether specific TCM integration may be beneficial or harmful for specific subtypes of breast cancer. For example, triple negative breast cancer has the highest mortality yet no one study reviewed investigated the use of TCM herb use on the outcomes in women with triple negative breast cancer. Furthermore, the current literature lacks specificity on TCM herbal use and chemotherapy dosing so we cannot know whether the observed survival benefit was related to TCM herbal use specifically or mediated via improved adherence to chemotherapy or hormonal therapy as a result of better symptom control. By more focused investigation of specific TCM herbal regimens in the context of specific conventional oncological treatment for specific subtypes of breast cancer, we can more precisely quantify the benefit and harm of TCM integration in oncology care and guide evidence-based care. Our review itself has important limitations, as well. The fact that different studies assessed different co-variates and potential confounders complicates the interpretation of results across studies. So too, the aforementioned heterogeneity in study designs, populations, and outcomes precluded pooling of data. Additionally, our review was limited to Taiwanese studies using the NHIRD database, which raises concerns about the generalizability of the review’s findings to other populations.

Breast cancer is the most commonly diagnosed malignancy in women worldwide, accounting for 24.5% of all cancer cases globally.[ 1 ] In 2020 alone, 2.3 million women were diagnosed with breast cancer. Patients in western countries are increasingly turning to traditional Chinese medicine (TCM), including herbal supplements, in the hopes of preventing breast cancer or improving their odds of survival while undergoing conventional breast cancer treatments.[ 2 – 4 ] Notably, some preclinical research indicates that certain Chinese herbs possess anti-cancer properties, including inhibition of tumor growth, induction of apoptosis (cell death), and suppression of angiogenesis (blood vessel formation to tumors).[ 5 – 12 ] Similarly, some clinical trials and observational studies suggest that using TCM as an adjuvant therapy can enhance immune function, symptom relief, and quality of life among patients with breast cancer [ 13 – 19 ] – all of which may facilitate adherence to and effectiveness of conventional cancer therapies.[ 20 – 22 ] Yet many of these studies face critical methodological limitations, including small sample sizes, lack of standardized herbal formulations, and inadequate comparisons.[ 23 ] Access disparities are particularly problematic: wealthier individuals, or those with better education, and those in urban areas often have better access to TCM practitioners and high-quality herbal products, while others face barriers such as affordability, availability, and lack of culturally competent TCM providers.[ 24 , 25 ] These challenges make it difficult to draw definitive conclusions about the effectiveness of TCM for breast cancer prevention and survival. To shed light on this critical issue, we conducted a narrative review of epidemiological studies assessing TCM herbal use and breast cancer prevention and survival in Taiwan, where access to high-quality TCM herbs and conventional cancer treatments is universally available, free of charge (no co-payments), and rigorously documented in a national health insurance database[ 26 ]. This unique database thus offers a rich source of high-quality, large-scale data on TCM herbal use and cancer outcomes for patients across the socio-economic spectrum and help mitigate some of the bias related to access and cost in prior studies. Our goal was to scope the available Taiwanese evidence on TCM herbal use in breast cancer, focusing on both cancer prevention and mortality.