Heterogeneous gene alterations in primary breast cancer contribute to discordance between primary and asynchronous metastatic/recurrent sites: HER2 gene amplification and p53 mutation

The aim of the present study was to clarify differences in genetic events between primary breast cancers and asynchronous metastatic/recurrent lesions, by examining HER2 gene amplification and p53 mutation. The subjects were 44 breast cancer patients with asynchronous metastasis or recurrence. Synchronous metastases were excluded. HER2 overexpression and gene amplification were examined using immunohistochemistry and fluorescent in situ hybridization (FISH). P53 point mutation was examined by immunohistochemistry, laser-captured microdissection, PCR-single-strand conformation polymorphism, and a direct sequencing method. Immunohistochemistry showed that, for HER2, p53, ER and PgR, discordance rates between primary and recurrent tumor were 2 (4.5%), 1 (2.3%), 7 (15.9%) and 10 (22.7%), respectively. Two primary tumors with discordant HER2 overexpression were composed of at least two populations of carcinoma cells, with and without HER2 gene amplification. Distribution of HER2 gene amplification was consistent with protein overexpression. Corresponding recurrent tumors consisted of carcinoma cells without HER2 gene amplification. Of 6 recurrent tumors in which the primary carcinoma had a p53 point mutation, 3 tumors had identical mutations, 1 tumor had a different point mutation, and 2 tumors had no mutation. It was suspected that the latter 3 recurrent tumors comprised a minor component of the primary tumor. In the present study, we examined a large series of asynchronous recurrent tumors. A limited number of these tumors showed discordance between primary and recurrent tumors. Detailed observations revealed that cell populations present in recurrent tumors were also present in the primary tumors, although they comprised a minor component of the primary tumor. Heterogeneity of the primary tumor apparently contributed to discordance.