A number of studies have been conducted on the possible role of an infectious agent in the causation of breast cancer. These studies have suggested the possible role of a virus related to a rodent borne mouse mammary tumour virus (MMTV; http://en.wikipedia.org/wiki/Mouse_mammary_tumor_virus) in association with human breast cancer tumours. The investigators identified a "..complete proviral sequence that was greater than 95% homologous to MMTV was sequenced out of human breast cancer tissue including a correct integration into the human genome." It was thence named Human Mammary Tumor Virus (HMTV). HMTV is a retrovirus (HIV is also a retrovirus) that inserts itself into human DNA and causes expression of a number of proteins that can alter hormonal levels and lead to subsequent tumour development.
HMTV may also be linked with other human diseases including leukemia since human breast cancer has been correlated with leukemia and HTMV's viral sequence has been found in this form of cancer.
Few if any studies have been conducted in rodents and the incidence of MMTV in localised mice populations. A number of other factors have been linked to increased risks of developing breast cancer including use of birth control pills, diet, lack of exercise, obesity, age at time of child birth, environmental exposure to carcinogens etc. Is there a mode of transmission from mice to humans where tumours are associated with HMTV? Only sound scientific evidence would be able to substantiate this.
To establish such evidence investigations of mice reservoir should be conducted to determine MMTV incidence within a localized region and or country. The samples obtained should yield good genomic data that could be used at a later date for comparison with viral DNA from human breast cancer tumours to determine the degree of viral strain relatedness.
Human studies using breast cancer tissues and normal tissues should be conducted to determine the incidence in humans both in the affected population and normal healthy population.
HMTV viral data should be compared with those already deposited in GenBank to assess relatedness with HMTV strains found in other parts of the world. Mice have a wide global geographical distribution yet there appears to be higher breast cancer incidence in populations of African descent than in Native American, Asian or Caucausian populations. The role of BRCA genes has partially explained this disparity but it remains to be seen if HMTV inserted into DNA of affected individuals is responsible for the switching on and off critical molecular pathways that alter hormonal levels in the body promoting tumour development.
It would be advantageous if such research is lent the necessary support that would allow a clearer perspective on this disease that affects millions worldwide.
No comments:
Post a Comment