Pleomorphic Carcinoma of the Colon: Morphological and Immunohistochemical Findings

Pleomorphic carcinoma is an aggressive neoplasm defined by the World Health Organization (WHO) as a poorly differentiated (squamous cell carcinoma or adenocarcinoma) or undifferentiated carcinoma in which at least 10% spindle and/or giant cells are identified, or as a carcinoma constituted purely of spindle and giant cells. Although this entity has initially been shown in the lung, it has been described also in extrapulmonary locations, with only one report for a colonic site. A 65-year-old woman developed a caecal tumour. Gross examination revealed an endophytic/ulcerative mass 7 cm in length. Microscopically, the tumour was a poorly differentiated adenocarcinoma with a pleomorphic component that occupied more than 10% of the specimen. The tumour shared these histopathological findings with pulmonary giant cell carcinoma but differed in other clinicopathological features such as a pushing growth pattern, stage pT3N1, and an uneventful outcome 24 months after operation. The pleomorphic component showed morphological and immunohistochemical features compatible with mitotic catastrophe, a non-apoptotic cell death occurring in cycling cells after aberrant mitosis. These features included multinucleation, micronucleation, atypical mitoses, foci of geographic necrosis, as well as immunohistochemical overexpression of p53 and Ki-67. The interpretation of the pleomorphic component as morphological expression of mitotic catastrophe may be useful in comprehending the pathogenesis of this rare neoplasm, and it may have practical implications as a potential cancer therapeutic target.