Table 2.
Comparative evidence.
| Mouse mammary tumor virus (MMTV) | Mouse mammary tumors | Human breast cancer |
|---|---|---|
| MMTV nucleotide and gene sequences | Complete MMTV genome of 9,900 base pairs identified (99–101) | Almost complete MMTV genome identified with 84–99% homology with mouse MMTV genome (45, 46). MMTV identification confirmed by whole-genome sequencing (45) |
| MMTV virus particles | MMTV virus particles visualized in mouse milk (99) | MMTV virus particles visualized in human milk (99) |
| MMTV breast cancer prevalence | MMTV identified globally in mouse mammary tumors (36) | MMTV-like virus identified globally in breast cancers (36) |
| Cancer-related gene expression | Same cancer genes deregulated in mouse mammary tumors and human breast cancer (51, 52) | Same cancer genes deregulated in mouse mammary tumors and human breast cancer (51, 52) |
| Temporality—MMTV infection time sequence | MMTV present in 0–50% of wild mice. 1% develop breast cancer (102, 103) | MMTV present in prior benign breast later breast cancer (37) |
| MMTV protein expression | MMTV proteins expressed (8, 104) | MMTV proteins expressed (53) |
| MMTV superantigen expression (SAg) | MMTV SAg plays an essential role in MMTV mouse breast cancer (60) | Human T cells respond to MMTV SAg (61). MMTV-like SAg identified in human breast cancer (61) |
| MMTV serum antibodies | Positive serological response to MMTV (105) | Positive serological response to MMTV (56–58). Serology not confirmed (59) |
| Hormone responsiveness | Mouse mammary tumors hormone dependent (8) | MMTV hormonal response elements promote cell growth (66) |
| MMTV transmission | MMTV transmitted by mouse milk to pups, which develop mouse mammary tumors as adult mice (8). MMTV present in mouse salivary gland—possible route of transfer (106) | Potential transmission by human milk and human saliva (72–74) |
| Infection experiments | Exogenous MMTVs target dendritic cells and B lymphocytes in intestinal lymphocytes and mouse mammary cells (8) | MMTV infects intestinal lymphocytes, human breast cells and randomly integrates into human genome (67, 68, 70, 107) |
| MMTV morphology | Classical MMTV mammary tumor morphology—Dunn types A and B (79) | Some MMTV positive breast cancers similar to MMTV positive mouse mammary tumors (30, 78) |
MMTV-associated human breast cancer and MMTV-associated mouse mammary tumors.