Improved prognosis of solid‐type poorly differentiated colorectal adenocarcinoma: a clinicopathological and immunohistochemical study

Aims: We rarely encounter solid‐type poorly differentiated colorectal carcinoma, and their histogenesis and biological behaviour are not fully disclosed. Methods and results: A review of 60 poorly differentiated carcinomas of the colorectum was undertaken, 36 (59%) of which were located in the right side of the colorectum. Although, on the basis of the World Health Organization (WHO) classification solid carcinomas are included among undifferentiated carcinomas, the poorly differentiated carcinomas were divided into four types; 27 solid carcinomas (Sol.), 17 poorly differentiated adenocarcinomas (PDA), six signet‐ring cell carcinomas (Sig.) and 10 mucinous carcinomas (Muc.). Solid carcinomas revealed a solid alveolar growth of fairly uniformly sized tumour cells with occasional mitotic figures. This type of tumour had a relatively lower percentage of lymphatic permeation and lymph node metastasis compared with the other three types. The 5‐year survival rates were 31% for all poorly differentiated carcinomas, 47% for the Sol. type, 32% for the PDA type, and 0% for both the Sig. and the Muc. types, with a rate of 72% for well‐differentiated adenocarcinomas selected as controls. Immunohistochemically, bcl‐2 protein expression was demonstrated in 38% of the Sol. type, but in only 12 % of the other three non‐solid types, this difference being significant (P < 0.05). Conclusions: These findings suggest that solid carcinomas of the colorectum should be regarded as a distinct type of poorly differentiated carcinoma, leading to a good prognosis.