• HUMAN MAMMARY TUMOR VIRUS (HMTV)

Breast cancer is the most common cancer in women and in the 35-55 age range is the principal cause of death amongst women worldwide. It has become clear that the clinical onset of breast cancer is influenced by several factors. Among these, the potential involvement of a virus of the family Retroviridae, the Human Mammary Tumor Virus (HMTV), has represented a major focus of investigation whose existence has been proposed and disputed for many years after the identification of the MMTV (Murine Mammary Tumor Virus). Several scientists were able to demonstrate the presence of HMTVenv sequence (HMTVes) in 30-40% of invasive human breast carcinomas and very recently our laboratory was able to prove that its presence is strictly associated with sporadic breast cancer progression.
In the present study we decide to add more evidence to the possible viral etiology of human breast cancer by approaching the problem from different angles:
1) the fact that in hereditary breast cancer (HBC) inherited gene mutations are recognized as initiating event led us to hypothesize that in this group an involvement of an oncogenic virus is not expected. The presence of MMTVes was investigated in a group of HBC from patients hosting a BRCA1 or BRCA2 mutations as well as in a group of SBC, with the aim to prove this hypothesis.
2) we decided to investigate the frequency of HMTVes in a set of sporadic breast cancer (SBC) samples collected in three different and geographically distant countries such as Sardinia, Jordan and Australia. In the last population when possible we collected also for each SBC case, a normal and pre-invasive lesion in order to assess the presence of the virus before cancer onset.
3) because the infiltrative carcinoma of the breast initially spreads via lymphatics giving metastasis firstly to the axillary and internal mammary lymph nodes, it was interesting to analyze lymph nodes of HMTVes positive and negative (HMTVes+ and -) tumors. From each metastatic lymph node was microdissected the tumoral epithelial cell population and the lymphocytes.
4) a gene expression study, using specific breast cancer arrays and a panel of selected genes, was performed to assess the genetic background in SBC HMTVes+ and – tumors and matched normal.
5) because of the strong similarities between the human and the murine disease, the presence of the MMTV virus in all murine exocrine glands led us to investigate if we could find HMTVes also in human saliva and salivary glands.
6) we have created HMTVes+ breast cancer cell primary cultures, from fresh human breast cancer tissues collected from the surgery-room in order to isolate the virus and FISH, Electron microscopy, Immunocytochemistry and Western experiments were performed to confirm the presence of the virus.
The results obtained from all experiments support our recent findings and also our new hypotheses. We were able to obtain only one HMTVes+ primary cancer cell line which seemed to be HMTV positive also by electron microscopy, FISH, immunocytochemistry and Western Blot analysis.