Post‐biopsy breast carcinoma: A natural experiment in cancer immunology

Prior studies suggested that patients with in‐situ breast cancer are characterized by particularly high levels of prognostically favorable immunologic responses. If second breast cancers arising in such patients are antigenically similar, one would expect such cancers to exhibit particularly favorable stage and survival characteristics. Breast cancers arising in patients having a history of precancerous mastopathy were found to have more favorable stage and survival characteristics than breast cancers preceded by normotypic benign lesions, prior invasive cancers, or unselected breast cancers. The findings are consistent with the existence of cross‐reacting immunologic responses in patients with in‐situ breast cancer. Negative findings in this natural experiment would raise serious questions regarding the ultimate development of effective immunoprophylaxis or immunotherapy of breast cancer.