Gastrointestinal stromal tumors (GIST) are a heterogeneous group of neoplasms whose biologic behavior is difficult to predict. The aim of this study is to evaluate the prognostic value in GIST of some oncoproteins involved in regulation of cell proliferation. Tumor size, mitosis, necrosis, and p53, c-myc, and bcl-2 protein expression of 32 GIST were studied. Proliferative index was assessed with Ki67. The 32 cases were grouped into the following clinical categories: (1) clinically benign (BN) were defined as disease-free survival greater than 3 years (n=10); (2) clinically malignant (MN) in which local recurrence or metastasis occurred regardless of the follow-up time (n=1 5); and (3) clinically indeterminate (ID) owing to follow-up <3 years without metastasis or local recurrence (n=seven). Discriminant analysis was used to allocate any tumor to one of the two prognostic groups (BN or MN). In univariate analysis all six factors studied above proved to be of significant prognostic value. Using a multivariate stepwise discriminant analysis to take into account the interrelationship between factors, we found that c-myc expression was the most important prognostic factor, followed, in order of statistical weight, by size and Ki67. These were combined to define a discriminant score ([10.75 x c-myc]+[0.39 x size]+[0.078 x Ki67]-15.54=score), which was capable of correctly identifying tumors in our series whose known clinical behavior was BN or MN in 92% of the cases. The classification score was applied subsequently to the seven clinically ID cases: Three (42.9%) were predicted as BN, and four (57.1%) were predicted as MN. Both expression of oncoprotein c-myc and the proliferative index provide prognostic information in GIST, in addition to morphologically established prognostic factors such as size. These factors in a discriminant analysis proved to be useful for the clinical classification of GIST into BN or MN and to predict the clinical outcome of clinically ID tumors.

This report describes an intraabdominal small cell tumor in a 37-year-old woman, with clinical, topographic, and morphologic features highly suggestive of the desmoplastic small round cell tumor. Immunohistochemical analysis revealed a polyphenotypic profile consistent with this tumor--positivity for keratin, epithelial membrane antigen, neuron-specific enolase, vimentin, and desmin--but, in addition, a strong membranous immunoreactivity for CD99 (MIC2 protein). Reverse transcription polymerase chain reaction revealed a EWS/ERG fusion transcript characteristic of the Ewing's sarcoma/peripheral primitive neuroectodermal tumor group of tumors, rather than the EWS/WT1 chimeric transcript typical of the desmoplastic small round cell tumor. This is the third report of a hybrid tumor with features of the desmoplastic small round cell tumor and Ewing's sarcoma/peripheral primitive neuroectodermal tumor, and the first one with the EWS/ERG fusion gene. Our case shows the existence of some overlap between these two groups of tumors, which are considered to be histogenetically different, and the need for further studies of molecular characterization of small cell tumors, especially in those with atypical morphologic or immunohistochemical features.

BACKGROUND The distinction between pleural mesothelioma (MS), reactive mesothelium (RM), and adenocarcinoma (AC) in serous effusions continues as a diagnostic problem in pathology. Immunohistochemistry can help, especially in surgical samples, but the optimum panel of antibodies has yet to be reported. The application of these antibodies to serous effusions has displayed variable results. The aim of this study was to evaluate the usefulness of eight monoclonal antibodies in the differential diagnosis of MS, RM, and AC in serous effusions. METHODS A total of 44 cytologic specimens of serous effusions (26 pleural, 15 peritoneal, and 3 pericardial) from 30 ACs, 3 MSs, and 11 RMs, previously stained with Papanicolaou stain, were selected retrospectively from our files and stained with HBME‐1, thrombomodulin, calretinin, MOC‐31, Ber‐EP4, E‐cadherin, CEA, and CD‐15. The immunoreactions were evaluated independently by two pathologists. A stepwise logistic regression analysis was applied to the data to select an appropriate panel of antibodies. RESULTS Statistical significance was found with HBME‐1, thrombomodulin, MOC‐31, Ber‐EP4, and CD‐15, when comparing both AC versus MS, and AC versus any type of mesothelial proliferation (MS or RM). Using HBME‐1, 80% of ACs were negative whereas all three MSs reacted strongly with P = 0.003. A P = 0.02 was reached with thrombomodulin with 76.5% of ACs showing no immunoreactivity. Ber‐EP4 and MOC‐31 displayed good results with a P < 0.001 and 0.01, respectively. CD‐15 reached a P = 0.034. No differences were found using the other antibodies. Ten ACs, all 3 MSs, and 10 RMs were double immunostained with HBME‐1 and/or MOC‐31 and Ber‐EP4 successfully. CONCLUSIONS Immunohistochemical studies performed on Papanicolaou stained cytologic smears proved to be useful in the differentiation between metastatic AC and mesothelial proliferation. HBME‐1, thrombomodulin, MOC‐31, Ber‐EP4, and CD‐15 were the most useful. In selected cases, it appeared that double immunostaining aided the differential diagnosis. Cancer (Cancer Cytopathol) 2001;93:68–72. © 2001 American Cancer Society.