CD4 and breast cancer: Previous studies have demonstrated that higher levels of tumor-infiltrating lymphocytes (TILs) are associated with improved prognosis in patients with breast cancer, non-small cell lung cancer, ovarian cancer, and other solid tumors, and the expression of different subsets of TILs correlates with patient survival.[29–32] An animal model of malignant melanoma showed that CD4+ T lymphocyte infiltration could lead to tumor regression.