The morphologic differentiation between clear-cell carcinoma and endodermal sinus tumors is difficult at times. To improve the accuracy of the diagnosis, the authors studied nine ovarian and eight vaginal clear-cell carcinomas and seven endodermal sinus tumors of the ovary by immunohistochemical methods with the use of antibodies to alpha-fetoprotein and Leu-M1. Sixteen (94.1%) of the 17 clear-cell carcinomas and two (28.5%) of the seven endodermal sinus tumors reacted for Leu-M1, whereas six (85.7%) of the seven endodermal sinus tumors and three (17.6%) of the 17 clear-cell carcinomas stained for alpha-fetoprotein. Three clear-cell carcinomas and two endodermal sinus tumors showed immunoreactivity for both markers. No reactivity for either of these markers was present in one endodermal sinus tumor and one clear-cell carcinoma. All 13 tumors that stained only for Leu-M1 proved to be clear-cell carcinomas, and the four that reacted exclusively for alpha-fetoprotein were endodermal sinus tumors. Therefore, the authors concluded that positive immunostaining for Leu-M1 and negative immunostaining for alpha-fetoprotein support the differential diagnosis of clear-cell carcinoma, whereas a positive reaction for alpha-fetoprotein and a negative reaction for Leu-M1 favor a diagnosis of endodermal sinus tumor. However, positive or negative staining for both markers appears to have no diagnostic value.

Four cases of primary non‐Hodgkin's lymphoma (NHL) of the thyroid were studied using flow cytometric (FCM) DNA analysis of propidium iodide‐stained nuclei retrieved from formalin‐fixed, paraffin‐embedded tissue. Two of the four cases were aneuploid and two were euploid. In the two euploid cases, both patients are alive and without evidence of recurrent disease after an average of 4 years follow‐up. Of the two aneuploid cases, one patient is alive and free of recurrent disease after 1 year. In the other aneuploid case, the patient died of disseminated disease 8 months after presentation despite having a low‐grade (follicular, predominantly small cleaved cell type) and low‐stage (tumor confined to thyroid at presentation) lymphoma. These data suggest that the DNA ploidy of primary NHL of the thyroid can be determined using fixed, paraffin‐embedded tissue. Our results also suggest that a large study to assess the prognostic value of this technique is warranted.