In order to document a possible involvement of structural alterations of FGF (Fibroblast Growth Factor)-like genes in human oncogenesis, we have screened a large series of human tumors for amplification of five FGF-related genes (Basic-FGF, INT2, HST, FGF5 and FGF6). None of 37 hematopoietic neoplasms, one out of 13 melanomas (8%), three out of 43 bladder tumors (7%) and 41 out of 238 breast carcinomas (17%) contained amplified FGF-related sequences, namely HST and INT2. Only these two genes, both located on band q13 of chromosome 11 have been found amplified. In all cases they were co-amplified and in only one instance did amplification extend to the ETS1 locus at position 11q23. INT2 and HST RNA could be evidenced by RNA/RNA in situ hybridization in breast carcinomas. Our results indicate a correlation between RNA expression and gene amplification in the case of HST but not of INT2. Although evaluation of the clinical significance of HST amplification and expression must await long-term follow-up of the patients, we suggest that HST gene product could play a role in development and/or progression of human breast cancer.