KIR2DL3/C1 was the only interaction that a showed lower frequency in BC patients treated with BCG (61.8%, p < 0.001) than in healthy controls (75.8%), in BC patients treated with other therapies (68.9%), and in other cancer patients (70.2%); therefore, the KIR2DL3/C1 interaction appeared to protect against low-stage BC. This evidence concerns the gene KIR2DL3 and breast cancer.