In pursuit of the primary

This case report highlights the rare occurrence of an EOPPC presenting as a massive pleural effusion in the absence of ascites. The diagnosis of a rare tumour like EOPPC can be challenging, since occult peritoneal disease can be difficult to detect on standard CT imaging. Furthermore, when the tumour presents solely with features of distant metastases, histopathological examination (including immunohistochemistry) becomes indispensable in identifying the source of the metastatic disease. Pleural fluid cell blocks can provide an inexpensive and less invasive method of obtaining a specimen for histopathological evaluation. EOPPC, a rare tumour can present with peritoneal deposits and MPE. CA-125 is an invaluable tumour marker and when elevated (even with normal ovaries on imaging) may indicate suspicion of EOPPC. Cell block of pleural fluid samples is an underutilised modality which when used judiciously can help in locating a clinically occult primary.

MPE involves invasion of malignant cells into the pleural tissue and is diagnostic of advanced cancer. The median survival following the detection of an MPE is 3–12 months, depending on the underlying malignancy, which in >80% of cases can be attributed to a lung, breast, gastrointestinal or genitourinary malignancy, or a lymphoma. ∼11% of MPEs arise from an unknown primary tumour [ 8 ]. EOPPC is a rare tumour and an even rarer cause of MPE. Between 1995 to 2004, the tumour itself was reported to have an incidence of 6.78 per million in the USA and the worldwide incidence is unknown [ 9 ]. EOPPC commonly presents with gastrointestinal symptoms, abdominal distension and pain (secondary to malignant ascites), and respiratory complaints are uncommon at presentation [ 7 ]. Metastasis in EOPPC occurs mainly transperitoneally but may also occur by lymphatic and haematological routes; and metastases to cervical lymph nodes, the breast, the brain and the lungs have been reported in the literature [ 10 – 13 ]. To the best of our knowledge, there have been only four other case reports in the English-language literature documenting EOPPC presenting with a pleural effusion [ 14 – 17 ]. Two of these reported patients who presented with dyspnoea secondary to massive pleural effusions in the absence of ascites or with minimal ascites, which is unusual. In these cases, the localisation of the primary tumour was aided by the findings seen on contrast-enhanced CT of the abdomen, and the diagnosis of EOPPC was established by a laparoscopic peritoneal biopsy and surgical pleural biopsy [ 14 , 15 ]. D ietrich et al. [ 16 ] also reported a case of EOPPC presenting with tension hydrothorax; however, their patient was found to have large ascites on further evaluation. Up to 81% of EOPPC cases are reported to have ascites at laparotomy; however, no ascites was detected in our patient pre-operatively on abdominal ultrasonogram or on PET-CT [ 7 ]. The National Institute for Health and Care Excellence has defined the entity “metastatic malignancy of undefined primary origin” as a “metastatic malignancy identified on the basis of a limited number of tests, without an obvious primary site, before comprehensive investigation” [ 18 ]. There is no universal consensus on the exact nature of these limited tests. The guidelines recommend standard histological examination of a biopsy specimen and basic immunohistochemistry (to establish if the malignancy is epithelial or nonepithelial in origin) in the initial line of investigations. In patients such as ours, who present with metastatic pleural involvement, the pleural fluid cell block can be used to perform this basic immunohistochemistry, as the sample can be obtained through a simple, inexpensive and less invasive procedure. Although the diagnostic yield of a thoracoscopic pleural biopsy has been reported to be superior to that of the pleural fluid cell block (94.2% versus 71.4%), the cell block can serve as an ideal initial sample and as a useful adjunct in diagnosis [ 19 ]. In carcinoma of unknown primary syndromes, P omjanski et al. [ 20 ] reported correct identification of 85.5% of primary tumour sites by using a panel of six immunocytochemical markers (CK5/6, CK7, CK20, CA-125, TTF-1 and caudal-type homeobox 2) to evaluate metastatic effusions.