Colorectal neuroendocrine carcinoma with squamous cell differentiation: a rare and unusual tumour

Abstract

Background: Neuroendocrine carcinoma (NEC) of the colorectum is rare, accounting for 0.4% of all colorectal neoplasms.1 Squamous cell carcinoma (SCC) of the gastrointestinal tract is also a rare entity and accounts for 0.1–0.25% per 1000 cases of colorectal carcinoma.2 World Health Organization (WHO) classification defines mixed adeno-neuro-endocrine carcinoma as a neoplasm with both exocrine and neuroendocrine components, with each component exceeding 30%. Aim: We present a rare case of a patient with colorectal neuroendocrine carcinoma with squamous differentiation. Method: An 86-year-old gentleman presented with right sided abdominal pain. A colonic mass was noted on CT scan with multiple liver lesions. Subsequent right hemicolectomy revealed an obstructive hepatic flexure tumour. Results and conclusions: Histopathological examination of the mass revealed a high grade neuroendocrine carcinoma (NEC) with diffuse sheets and cords of epithelial cells with crowded nuclei, scant cytoplasm and frequent mitotic figures (23 per 10 high-power field). Amongst the NEC component, small areas (less than 30% of the tumour volume) comprising larger epithelial cells with abundant eosinophilic cytoplasm and areas suggestive of keratinisation were noted. The NEC component was positive for synaptophysin and CD56 immunohistochemistry with a Ki67 proliferation index of 80–90% and negative for P40 and CK5/6 immunohistochemistry. In contrast, the areas with large eosinophilic cells were positive for P40 and CK5/6 immunohistochemistry, whilst negative for synaptophysin and CD56 immunohistochemistry. The tumour exhibited aggressive behaviour with lymphovascular, perineural and venous invasion and lymph node metastases. Neuroendocrine carcinomas and squamous cell carcinomas of the colorectum are rare and extremely aggressive neoplasms3 on their own merits. This phenomenon of mixed neuroendocrine carcinoma with squamous cell differentiation is an unusual and rare pathology which lacks evidence-based guidelines for therapy. It is worth documenting as the optimal therapeutic strategy remains the main challenge.