Intratumoral heterogeneity for amplified genes in human breast carcinoma

Intratumoral heterogeneity was studied in human breast cancer by examining separate tumor lesions of individual patients. Tumor samples were obtained from each patient by fine-needle biopsies from 2 to 4 separate tumor lesions. We used a semi-quantitative PCR to distinguish between samples with gene amplification and single gene copy samples. Five genes were analyzed in each biopsy: MDR-1, dihydrofolate reductase, thymidylate synthase, c-erb-B2 and int-2. Three groups of patients were examined: those awaiting initiation of treatment; those receiving first-line endocrine therapy; and those receiving second-line endocrine treatment. A pattern of intratumoral heterogeneity for gene amplification was clearly apparent. The frequency of amplification was lowest before initiating therapy and highest in patients receiving second-line treatment (p = 0.023).