Clear cell colorectal carcinoma: Time to clarify diagnosis.

Primary clear cell colorectal carcinoma (CCC) is a very rare entity accounting for only 35 cases reported in the Literature. CCC is neither classified as a distinct entity nor is it defined as a CRC variant because its ontogeny remains unclear. Most of the reported CCC were found in the distal colon in patients with a mean age of 56 years. Histologically, clear cell change is the main morphologic feature and may present in a "pure" form, composed exclusively of clear cells, or in a "composite" form, admixed with other morphologically different components. It is possible to distinguish two biologically different types of CCC, with different clinical-pathologic features, therapeutic management and diagnostic criteria: a) Intestinal CCC consisting of an aggressive neoplasm, affecting mainly adult men, characterized by an intestinal-type immunoprofile (CK20+, CK7-, CEA+, CDX-2+) and b) Müllerian CCC consisting of an indolent carcinoma of the sigmoid-rectum, affecting young women, characterized by a different (CK7+, CK20-, CEA-, CA125 +) immunoprofile. Considerable diagnostic difficulties can arise in distinguishing CCC and primary or secondary clear cell neoplasms, such as metastases from renal carcinoma, lower urinary tract, female genital tract, adrenal gland, mesothelioma, melanoma and primary intestinal PEComa. In this paper we review the Literature with two additional cases in order to define the diagnostic criteria of CCC.