Postchemotherapy Endometrioid to Gastrointestinal Histotype Shift in Recurrent Endometrial Carcinoma

: Herein, we report a case of low-grade endometrial endometrioid carcinoma recurred on the vaginal stump, which showed a complete histotype shift toward a gastrointestinal-type carcinoma after chemotherapy. The recurrent tumor increased in volume during chemotherapy. Postchemotherapy histologic examination showed a pure mucinous signet-ring cell pattern with positivity for cytokeratin 20 and CDX2, focal SATB2 expression and negativity for cytokeratin 7 and estrogen and progesterone receptors. Such features led to consider a diagnosis of metastasis from a primary carcinoma of the gastrointestinal tract. The accurate exclusion of any primary lesions of gastrointestinal and of other sites allowed identifying the tumor as the recurrent endometrial carcinoma. Our case highlights that chemotherapy may induce a histotype shift from endometrioid carcinoma to gastrointestinal-type carcinoma; such occurrence might be a mechanism of resistance and might provide new insights on the sensitiveness of different histotypes to systemic therapies. Considering the possibility of a shift from endometrioid to gastrointestinal-type carcinoma may be useful for a correct diagnosis and an appropriate patient management.