The significance of squamous differentiation in endometrial carcinoma. Data from a Gynecologic Oncology Group study.

Squamous differentiation is identified in about 25% of endometrial adenocarcinomas (AC). Its significance has been the subject of debate for decades, and it has been reported that the prognosis of adenoacanthoma (AA) is better than, the same as, and worse than that of AC. Part of this confusion has resulted from semantic differences relating to the use of AA and adenosquamous carcinoma (AS). To investigate the prognostic importance of squamous differentiation in endometrial carcinomas and compare the prognostic utility of two classification systems, 456 women were studied who had typical AC and 175 women who had typical AC containing areas of squamous differentiation (AC + SQ) and who had been entered in a Gynecologic Oncology Group protocol of Stage I and II endometrial adenocarcinoma. Assessment of histologic grade and depth of invasion was done both by the pathologist at the member institution and at a second highly structured review. Differentiation of the squamous component of endometrial carcinomas was found to parallel that of the glandular component in most tumors. The biologic behavior of endometrial carcinomas with squamous elements was similar, but not identical, to that of typical AC. Although the frequency of nodal metastasis was similar for both AC and AC + SQ, the presence of squamous elements was associated with an increased probability of survival. Division of AC + SQ by depth of myometrial invasion and by architectural grade of the glandular component provided useful prognostic information that was superior to that resulting simply from division of AC + SQ into AA or AS. The authors recommend that these terms be replaced by "adenocarcinoma with squamous differentiation" and that the pathologist provide information on the architectural grade and depth of myometrial invasion to guide the gynecologist in determining appropriate therapy.