Abstract
BACKGROUND: Mouse mammary tumour viruses (MMTVs) may have a role in a subset of human breast cancers. MMTV positive human breast cancers have similar histological characteristics to neuroendocrine breast cancers and to MMTV positive mouse mammary tumours. The purpose of this study was to investigate the expression of neuroendocrine biomarkers - synaptophysin and chromogranin, to determine if these histological characteristics and biomarker expression were due to the influences of MMTV. METHODS: Immunohistochemistry analyses to identify synaptophysin and chromogranin were conducted on a series of human breast cancers in which (i) MMTV had been previously identified and had similar histological characteristics to MMTV positive mouse mammary tumours and (ii) MMTV positive mouse mammary tumours. RESULTS: The expression of synaptophysin and chromogranin in MMTV positive mouse mammary tumors were all positive (7 of 7 specimens - 100% positive). The expression of synaptophysin and chromogranin in MMTV positive human breast cancers was much less prevalent (3 of 22 - 14%). There was no expression of synaptophysin and chromogranin in the normal breast tissue control specimens. DISCUSSION: It is not possible to draw any firm conclusions from these observations. However, despite the small numbers of MMTV positive mouse mammary tumours in this study, the universal expression in these specimens of synaptophysin and chromogranin proteins is striking. This pattern of synaptophysin and chromogranin expression is very different from their expression in MMTV positive human breast cancers. The reason for these differences is not known. CONCLUSIONS: The high prevalence of positive expression of synaptophysin and chromogranin in MMTV positive mouse mammary tumours and low expression of synaptophysin and chromogranin in MMTV positive human breast cancers indicates that MMTV is not usually associated with neuroendocrine human breast cancers.