A retrovirus similar to MMTV associated with human breast cancer

We investigated whether a retrovirus similar to the mouse mammary tumor virus (MMTV) is implicated in human breast carcinogenesis.

Using PCR and specific primers, a 660-bp sequence homologous to the env gene of MMTV was detected in 38% of the human breast cancers. This sequence was absent in normal tissues and other tumors [1]. Samples from several geographical locations have higher or lower frequencies.

The MMTV-like sequence was expressed as RNA in most positive specimens [2]. The complete 9.9-kb proviral sequence of an MMTV-like agent has now been amplified and sequenced in two breast cancers. Structural features of this provirus suggest that it is replicative competent [3].

Primary cultures of env positive tumors show budding retroviral particles, and the supernatant particulate fractions show RT activity, presence of MMTV-like genes by RT-PCR and viral particles by electron microscopy [4]. Experiments to prove infectivity are in progress.

Whether this virus is MMTV or a related human mammary tumor virus is not certain, or is it known how humans are infected. However, if a retrovirus is indeed involved in human breast carcinogenesis, then preventive strategies can be planned.