Primary breast malignancies in adolescents and young adults: The MD Anderson Cancer Center experience.

10006 Background: Primary malignancies of the breast rarely affect adolescents and are uncommon in young adults. Limited information is available about their clinicopathologic characteristics and outcomes. The 5-year overall survival (OS) for women with breast cancer, not including ductal carcinoma in situ, exceeds 90%. However, it remains unclear whether adolescents and young adults experience similar outcomes compared with older patients. Methods: We conducted a retrospective study of all patients aged 0–25 years with primary breast malignancies seen at MD Anderson Cancer Center between 2000 and 2024. Demographics, histology, staging, treatment, and outcome data were collected. Event-free survival (EFS) and OS were estimated using the Kaplan–Meier method. Log-rank test was used to analyze patient outcomes by histology. Results: A total of 110 patients were identified. Median age at diagnosis was 23.9 years (range, 15.7–25.5). Two patients were male, 44.9% were White, 27.7% Hispanic, and 15.9% Black. The most common tumor histology was invasive ductal carcinoma (n=83, 75.5%), followed by sarcoma and malignant phyllodes tumors (n=14, 12.7%), carcinoma in situ (n=7, 6.4%), and rare histologic subtypes (n=6, 5.5%). Family history of breast cancer was present in 53.6% of patients and ovarian cancer in 9%. Of 81 patients with germline genetic testing, 25 (30.9%) had a cancer predisposition syndrome: Li-Fraumeni (n=9), BRCA1 (n=8), BRCA2 (n=4), ATM (n=2), other (n=2). Eleven patients (10%) had metastatic disease at presentation to bone, lung, distant lymph nodes, and liver. Among the 96 carcinoma cases, 36 (37.5%) were estrogen or progesterone receptor-positive and HER2-negative; 25 (26%) were HER2+, and 32 (33%) were triple-negative. Of the 110 patients, 69 (62.7%) received neoadjuvant chemotherapy, 37.6% of whom achieved a pathologic complete response, and 46.3% a partial response. Most patients (92.7%) had surgery (mastectomy 87.2% or lumpectomy 9.8%), 67.2% received radiotherapy, and 25.4% targeted therapy. Following treatment, 56 (51%) patients received adjuvant endocrine therapy. The 5-year EFS and OS for the cohort were 30% (95% CI, 22.6-39.9) and 71.8% (95% CI 62.9-82), respectively, and are presented by histology in the table. EFS (p=0.023) but not OS (p=0.36) was associated with histologic type. Conclusions: Primary breast malignancies in adolescents and young adults have distinct characteristics with a high frequency of family history and genetic predisposition syndromes and appear to be associated with lower survival compared with breast cancer in older patients. Histology No. of patients 5-year EFS (%) (95% CI) 5-year OS (%) (95% CI) Invasive ductal carcinoma 83 31.3 (22.8, 43.1) 68 (57.9, 80) Sarcoma and malignant phyllodes tumors 14 28.6 (12.5, 65.4) 82.1 (62.1, 100) Carcinoma in situ 7 42.9 (18.2, 100) 100 (100, 100) Rare histologic subtypes 6 NA 100 (100, 100)