Second primary malignancies in women with breast cancer.

Background: Increased screening and treatment advancements have resulted in improved survival rates in women with breast cancer (BC). However, recent data suggests these women have elevated risk of developing a second primary malignancy (SPM) compared to the general population. Limited data exists on factors associated with BC patients developing a SPM.
Method: A retrospective review of a prospective single institution database (1990-2016) identified 782 patients with a history of BC. One hundred and ninety-four BC patients developed a SPM. Clinicopathologic and treatment characteristics were analyzed.
Results: Of the 194 patients (24.8%) who developed a SPM, 56 (28.9%) BC patients were <50 years old (range: 24-87 years). Two-thirds (64.9%) had at least one first or second degree relative with a malignancy (no relatives-35.1%; ≥1 relative-62.9%). Most patients had invasive ductal carcinoma (n = 117, 60.3%) or ductal carcinoma in situ (n = 39, 20.1%). Twenty-two patients (11.3%) had pathogenic genetic mutations. Mean time to developing a SPM was 8.9 years (range: 4 months-50 years). Eighty (47.6%) patients received chemotherapy with 91 (54.5%) completing radiation. The most common SPMs were breast (22%), melanoma (17.8%), gynecologic (14.1%), colorectal (12.6%), hematologic (8.9%), and sarcoma (6.5%). Most breast tumors were estrogen receptor (ER) (n = 99, 78.0%) or progesterone receptor (PR) positive (n = 87, 73.1%) but not HER2-neu positive (n = 13, 14.0%).
Conclusion: Most BC patients who developed a SPM had ER/PR positive tumors and a family history of malignancy, with most <50 years old. Although chemotherapy and radiation increase cancer risk, there were an equal number of patients with SPMs who did or did not receive either treatment. Most SPMs were breast, soft tissue, gynecologic, hematologic, or colorectal. BC patients should be followed closely given an elevated propensity for developing SPMs.
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