EXTRAMEDULLARY MYELOID CELL TUMORS - AN IMMUNOHISTOCHEMICAL STUDY OF 29 CASES USING ROUTINELY FIXED AND PROCESSED PARAFFIN-EMBEDDED TISSUE-SECTIONS

Objective.-Extramedullary myeloid cell tumors (EMCTs) may be unsuspect ed clinically and difficult to recognize histologically. Fresh or froz en tissue is often not available for analysis. We studied 29 cases of EMCT using routinely fixed and processed paraffin-embedded tissue, an immunohistochemical method, and a panel of antibodies. Patients.-We st udied 29 patients with EMCTs: 22 males and 7 females, with a median ag e of 48 years (range, 5 to 80 years). Histologically, 9 tumors were we ll differentiated, 16 were poorly differentiated, and 4 were blastic. Results.-The Leder stain (napthol-ASD-chloroacetate esterase) was posi tive in 21 (77.7%) of 27 tumors. Immunohistochemically, the following antibodies reacted with the greatest number of cases: Leu-22 or MT1 (C D43) in 28 (96.6%) of 29, antilysozyme in 27 (96.4%) of 28, and antimy eloperoxidase (MP07) in 21 (91.3%) of 23 cases. Other myeloid lineage- associated antibodies were positive in a subset of cases: antineutroph il elastase (NP57) in 10 (62.5%) of 16, Leu-M1 (CD15) in 7 (46.6%) of 15, and Mac-387 in 6 (40.0%) of 15 cases. The well-differentiated EMCT s reacted with most myeloid-associated antibodies; poorly differentiat ed and blastic tumors were more often negative. The pan-leukocyte anti body LCA (CD45RB) reacted with 15 (60%) of 25 neoplasms. Three (16.6%) of 18 tumors contained numerous p53-positive cells, ranging from 10% to 50% of the tumor cell population, In 10 cases, exons 5 through 8 of the p53 gene were analyzed using the polymerase chain reaction and si ngle-stranded conformational polymorphism analysis. Gel shifts consist ent with mutations were identified in exon 8 of one tumor (10%) that e xhibited abundant p53 immunostaining. Conclusions.-lmmunohistochemical studies using fixed, paraffin-embedded sections are very useful in th e diagnosis of EMCTs. The most sensitive antibodies are anti-CD43, ant ilysozyme, and antimyeloperoxidase. Immunohistochemical methods are mo re sensitive than the Leder stain. We found p53 staining in a small su bset of cases, in which we were able to confirm evidence of p53 gene m utation using the polymerase chain reaction and single-stranded confor mational polymorphism analysis in one case; p53 gene mutations appear to be uncommon in EMCTs.