Oncocytic metaplasia and carcinoma of the endometrium: An immunohistochemical and ultrastructural study

Endometrial oncocytic carcinoma is an unusual neoplasm, with few cases repo rted. Endometrial curettage specimens coded as prominent oxyphilic metaplas ia (N = 5) and oxyphilic or oncocytic carcinoma (N = 4) were reviewed, and hysterectomy slides from the four carcinomas were also examined. Immunohist ochemical and ultrastructural analyses were performed in three of five meta plasias and in all four carcinomas. Most patients (89%) with oncocytic meta plasia and carcinoma had vaginal bleeding. Oncocytic metaplasia was charact erized by a single layer of cells with abundant eosinophilic, granular cyto plasm, minimal pleomorphism, and rare mitotic activity. Carcinoma was diagn osed on the basis of an altered stroma (n = 2) and/or a confluent growth pa ttern (n = 4) and had a papillary (n = 4), glandular (n = 2), or solid (n = 1) morphology. Carcinomas showed a similar population of oncocytic cells a s metaplasias, but with occasional nuclear stratification and greater pleom orphism and mitotic activity. Tumors were International Federation of Gynec ology and Obstetrics (FIGO) grade I (n = 2) or 2 (n = 2) and FIGO stage Ib, Ic, IIb, and IIIc. Omental metastases developed in the patient with the st age III tumor at 13 months; the two patients with stage I tumors were alive with no evidence of disease at a mean of 29 months. AU carcinomas expresse d p53 and 75% and 100% were estrogen receptor (ER)and progesterone receptor (PR)-negative, respectively, whereas all metaplasias were p53 negative-and ER- and PR-positive. Ki-67 labeling index was 1 to 3% in metaplasias and 1 4 to 33% in carcinomas. Oncocytic metaplasias and carcinomas contained abun dant mitochondria and free ribosomes, accounting for the oncocytic appearan ce. Because oncocytic carcinomas frequently show deep myometrial invasion a nd require surgical staging, it is important to distinguish oncocytic metap lasia from carcinoma on biopsy material. Ki-67, p53, and ER and PR immunost ains may assist in this potentially difficult differential.