Association of MMTV-like Sequences with Human Breast Cancer in Pakistani Population

Abstract

Breast cancer is the most common cancer in females and leading cause of cancer related deaths in females worldwide. Breast cancer is more common in developed countries as compared to developing countries. Even though Pakistan lies in the region of low prevalence of breast cancer there is substantially higher rate reported as compared to its neighbors. The known risk factors of breast cancer include mutations in P53 gene BRCA1 and BRCA2 genes, hormonal factors and lifestyle based factors. As reported for other cancers viral etiology of breast cancer is also suspected. Mammary tumors in mice are also caused by virus known as Mouse Mammary Tumor Virus (MMTV). The search for human homolog of MMTV gained direction when highly specific MMTV DNA sequences were shown to be present in human breast cancers. Different levels of association are reported from different regions of the world however there is no consensus on whether they present any risk to humans in regard with breast cancer or not. We hypothesized that among other risk factors viral infection may also contribute to development of breast cancer. In order to study the prevalence of MMTV-like sequences we collected blood and formalin fixed paraffin embedded breast cancer samples from Pakistan. We extracted the DNA and samples confirmed for DNA integrity by amplification of β-globin gene fragment. At the same time we also obtained tissue and blood sample from mouse to compare the two samples. MMTV sequences amplified from mouse were cloned into TA vector and sent for sequencing. While human breast cancer samples still need to be screened for prevalence of MMTV sequences