Colorectal carcinoma with dome-like phenotype: an under-recognised subset of colorectal carcinoma?

BACKGROUND

The term dome carcinoma has been applied to a variant of colorectal carcinoma, thought to derive from M-cells of the gut-associated lymphoid tissue. Its distinguishing morphological features include a non-polypoid plaque-like lesion composed of closely apposed cystically dilated glands lined by a single layer of non-mucinous cells, intensely PAS-positive intraluminal material, and a close spatial relation to lymphoid stroma.

AIMS AND METHODS

A search in the literature for such cases and the authors' experience with carcinomas sharing morphological details with dome carcinoma are presented to direct focus on this unique phenotype of colorectal carcinoma and to expand on its morphology.

RESULTS

Four such examples, all stage pT1, pN0 have been previously reported. Here two additional cases, with several features of dome carcinoma, stage pT1 and pT2, respectively, are added. An extensive intramucosal component, unassociated with adenomatous growth, a pink quality of the lesional cells, low grade budding, absence of cytoplasmic pseudofragments, and absence of necrosis characterised the present cases as well as intact MMR-proteins and loss of APC. As opposed to two of the previously reported cases, intraepithelial lymphocytes were unapparent in these cases and the lymphoid stroma was effaced along with tumour progression in one of the present cases. Hence, a range of appearances is encompassed by the dome carcinoma. The uncommon reporting of dome carcinoma may be due to lack of awareness of this particular subset of colorectal carcinoma. Indeed, one of the current cases was signed out as a conventional carcinoma, despite the comment in the pathology report of an unusual morphology.

CONCLUSION

Dome carcinoma may be more under-recognised than rare. The reporting of variants of colorectal carcinoma, displaying histological features suggestive of dome carcinoma, is encouraged in order to obtain more exact knowledge on its putative clinical significance.