Mouse Mammary Tumor-Like Virus Is Associated with p 53 Nuclear Accumulation and Progesterone Receptor Positivity but not Estrogen Positivity in Human Female Breast Cancer

Purpose: The purpose is to compare the presence of proteins with known associations with breast cancer— progesterone receptor (PgR), estrogen receptor, and p53, with the prevalence of mouse mammary tumor virus (MMTV)-like DNA sequences in human female breast cancers. Experimental Design: A cohort of 128 Australian female breast cancers were screened for MMTV-like DNA sequences using PCR. The presence of PgR, estrogen receptor, and nuclear accumulation of p53 protein was assessed in the same samples using immunohistochemical staining. Results: Nuclear accumulation of p53 was significantly more prevalent (P 0.05) in archival human breast cancers containing MMTV-like DNA sequences. The presence of progesterone receptor was significantly higher in MMTVpositive than MMTV-negative breast cancers (P 0.01). No correlation between estrogen receptor and MMTV-like DNA sequences was found. Conclusions: MMTV causes breast cancer in mice, and hormones up-regulate expression of virus in mice mammary tissue. It is unknown if this is the case in human breast cancers shown to contain DNA of MMTV-like viruses. The positive association between MMTV-like DNA sequences and PgR indicates hormones and MMTV may play a role in human breast cancer. Mutations of the tumor suppressor gene p53 are common in human breast cancer and are associated with higher grades of cancer. The association of MMTV-like DNA sequences with higher grades of cancer, and the positive association between p53 and MMTV-like DNA sequences clearly warrant additional investigation.