4T1

4T1 is a murine mammary carcinoma cell line derived from a spontaneous mammary tumor in a BALB/c mouse. The line is highly tumorigenic and metastatic, and it is widely used as a model of stage IV breast cancer in mice.

In research, 4T1 cells are typically orthotopically injected into the mammary fat pad of syngeneic female BALB/c mice. They form primary mammary tumors that readily metastasize to distant sites, most notably the lungs, but also to the liver and other organs, often without any surgical intervention to promote spread. This behavior makes 4T1 a popular model for studying metastasis and tumor-immune interactions in vivo.

The cell line generally exhibits a triple-negative phenotype, being estrogen receptor–negative and progesterone receptor–negative, with most lines also lacking HER2/neu expression. This basal-like character aligns with certain aggressive human breast cancers and supports its use in testing therapies aimed at triple-negative disease.

Because 4T1 grows in immunocompetent mice, it enables investigations into tumor microenvironment, immune evasion, and immunotherapeutic approaches, including vaccines, checkpoint inhibitors, and combination regimens. In vitro studies with 4T1 can reveal aspects of proliferation, invasion, and response to drugs, while in vivo work provides insight into metastatic progression and treatment effects.

Limitations include species differences that limit direct translation to human breast cancer; results from the 4T1 model should be interpreted with caution and complemented by additional models to corroborate findings.