Mucin 4 expression is associated with metastasis in triple-negative breast cancer and can be tackled by soluble TNF blockade, improving immunotherapy outcome.

Purpose: Triple-negative breast cancer (TNBC) has the worst prognosis among breast cancers. Immunotherapy is a therapeutic option, but there is no biomarker to guide promising combination treatments. Mucin 4 (MUC4) favors metastasis in preclinical cancer models.