Her-2 oncogene amplification, chromosome 17 and DNA ploidy status in synovial sarcoma

Abstract

The treatment options for synovial sarcoma (SS) are very limited, though this type of sarcoma seems to be more heterogeneous than it has been traditionally considered. The present study investigates the Her-2 oncogene status of 20 cases of SS, to determine whether Her-2 amplification can be considered as a prognostic factor. Her-2 oncogene amplification was determined on smears (frozen material was used from our tumor bank in each case), using fluorescence in situ hybridization technique (dual color FISH with centromeric probe for chromosome 17 and specific probe for Her-2 oncogene). Moreover, protein expression was assessed by immunohistochemistry, and DNA ploidy status was measured using image analysis. We had 5 biphasic and 15 monophasic SSs, patients’ age ranged from 13 to 68 years (mean, 39.8 years). Tumor size was larger than 5 cm in each case. Followup time ranged from 6 to 78 months (mean, 38.5 months). For statistical analysis the chi-square test was used. Her-2 oncogene amplification was found in three cases (15.0%) of 20 SSs. These cases proved to be 2+ positive by immunohistochemistry, but massive amplification, characteristic of a subset of breast carcinomas, was not observed. Her-2 oncogene amplification was significantly associated with a lower risk of developing metastasis (P<0.05) (none of the 3 amplified cases had metastases), while no association was found with recurrence. Six cases proved to be aneuploid and 14 were diploid, but no association was found between Her-2 amplification status and ploidy, and between ploidy status and metastasis or recurrence. Our results emphasize and confirm that Her-2 oncogene amplification is a rare event in SS, but the small subset of SS with Her-2 amplification has a better overall prognosis. Furthermore, this may open a theoretically new treatment possibility with Trastuzumab for Her-2-amplified cases of SS.