II. Lymphosarcomas
III. Respiratory Neoplasms
I. Mammary Tumors (Adenocarcinomas)
Mammary tumors (adenocarcinomas) are fairly common and may be located nearly anywhere in the subcutaneous region due to the extensive distribution of mammary tissue in the mouse (A.). They may be induced by mouse mammary tumor virus (or MMTV). There are multiple strains of MMTV and depending on strain, the virus can be transmitted by passage through the germline, placenta or in the milk. Mammary tumors are soft, fleshy, well vascularized and may contain necrotic tissue and/or blood-filled cysts. Histologically, mammary tumors are generally adenocarcinomas (B.). Mammary tumors may be surgically removed, but, unlike the benign fibroadenomas in rats, the prognosis is poor due to the anaplastic, invasive nature of the tumors in mice.
Lymphosarcoma is probably the second most common spontaneous neoplastic
disease, the incidence of which is dependent on the strain of mouse.
Lymphocytic, lymphoblastic, follicular center lymphosarcomas have been
described. C-type viral particles have been observed in murine lymphomas.
Benign respiratory tumors, primarily adenomas of the alveolar lining cells or of terminal bronchiolar epithelial cells, are common in certain strains (A strain) and older mice. Malignant neoplasms, such as squamous cell carcinoma, occur infrequently.
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