Is breast cancer in Barbados infectious?

The concept that a virus is involved in the genesis and development of breast cancer has been proposed and held in scientific discussions for many years. In fact Dr. Bittner in 1936 was the first to described the causative agent of breast cancer in mice, the mouse mammary tumour virus (MMTV).

Many studies in the 1970s and 1980s have proven the presence of MMTV-like sequences in breast cancer samples but the notable absence from normal breast tissues. Serological studies proved that antibodies raised against this virus could be found in breast cancer patients. Furthermore viral particles with characteristics of a retrovirus were observed in samples of breast milk (60%) from breast cancer patients.

However the possibility of a virus causing breast cancer has not been without challenges and scientific opposition. There were a number of studies failing to find the viral sequences in breast cancer samples which have been reported. One study presented data which showed that the human genome contains retroviral sequences that are 50% homologous to MMTV. Another study found MMTV like virus in a pool of 300 normal breast milk samples.

The possibility of DNA contamination from rodents namely mice was advanced as the reason for positive detection of these sequences and absences in other studies. The variation in detection could very well be due to variation due to geographical location.

Questions remain on the origin of MMTV sequences detected in human breast cancer. It has been suggested that these sequences represent a human form of MMTV, others have suggested that these sequences are not, in fact, a separate virus, but rather MMTV acting as a zoonotic virus.