A case of locally advanced adenosquamous carcinoma of the cecum with long-term survival.

Japanese clinical guidelines for colon cancer define ASC of the colon as a neoplasm that comprises adenocarcinoma and SCC. The histogenesis of ASC of the colon is not clearly understood, but three hypotheses have been suggested: (1) undifferentiated or reverse cells in the colonic epithelium may change directly into SCC; (2) secondary ASC derived from adenocarcinoma (currently, the most widely accepted explanation); and (3) ectopic squamous cells in the colonic mucosa may be directly transformed into squamous malignant cells. 3 , 4 ASC of the colon is rare, with an incidence of 0.1%−0.2% among all CRCs. 5 Masoomi et al. reported a population-based evaluation of ASC of the colon in the California Cancer Registry from 1994 to 2004; they found that out of 111,263 cases of CRC, ASC was identified in only 99 cases (0.09%). 6 The most common location was the proximal colon and the median age was 67 years, which is similar to our present case. As colorectal ASC tends to form both regional and distant metastases, its long-term prognosis is often unfavorable, with an overall 5-year survival rate of only 31%. A study of 576 patients with ASC in Taiwan showed 27 had colorectal ASC (0.04%); it found that colorectal ASC was most likely to affect the respiratory system (73.8%), followed by the alimentary canal (16.2%), and the female reproductive tract (10%), and that prognosis for ASC of the colon was much worse than for other primary ASCs. 7 , 8 Data from the National Institutes of Health also showed a poor prognosis, which Hijikawa et al. suggested was due to the very rapid growth of secondary ASC derived from adenocarcinoma. 4 Our present patient had no distant metastases, but as she had lymph node metastases and T4b tumor depth, she had a high risk of recurrence. She received adjuvant chemotherapy using CapeOX for colon adenocarcinoma; however, the exact role of adjuvant chemotherapy remains unclear. 9 In the present case, the patient developed early sigmoid colon cancer at 1 year after the first surgery and advanced breast cancer at 7 years after. Metachronous colon cancer is a criterion for Lynch syndrome in the Revised Bethesda guidelines. Raymond et al. reported the possibility of Lynch syndrome-associated breast and prostate cancers. 10 In the present case, the specimen was immunopositive for MLH1, PMS2, and MSH6; however, these proteins are not clearly described in the criteria and we conclude this case is not Lynch syndrome. Recently, Duncan et al. reported high microsatellite instability in ASC and ASC with Lynch syndrome. 11 – 13 As no biomarkers for diagnosis and prognosis are currently known, we should treat ASC as conventional adenocarcinoma. In the future, we expect genetic analysis using next-generation sequencing to assist in drug and treatment choice. Erik et al. reported molecular profiling of lung ASC. 14 Because of the rarity of colonic ASC, countrywide registry database systems and gene analysis programs are required.