Abstract PS7-60: Adenosquamous carcinoma of the breast: A population-based study using the SEER database

Background: The present study is aimed at summarizing the clinicopathological characteristics, prognosis, and management of breast adenosquamous carcinoma (ASC). Methods: A population-based study was performed using retrospectively extracted data from the Surveillance, Epidemiology and End Results database for breast cancer patients with histological diagnoses of ASC, infiltrating duct carcinoma (IDC) and squamous cell carcinoma (SCC) from 2004 to 2016. End-points were overall survival (OS) and breast cancer-specific mortality (BCSM). Propensity Score Matching (PSM) was employed to minimize selection bias of baseline characteristics. Univariable and multivariable analyses were used for identifying valuable prognostic factors. Results: ASC presented similar tumor size but low histological grade and less lymph node metastasis compared to IDC. ASC expressed less positive rate of hormone receptors and barely HER2, which was similar with SCC (estrogen receptor (ER): ASC 27.74% and SCC 21.53%, progesterone receptor (PR): ASC 18.06% and SCC 12.85%, HER2: ASC 4.44% and SCC 7.53%). ASC patients underwent the same treatment as IDC (chemotherapy 36.99% vs. 41.86%, BCS 50.58% vs 52.83%, P >0.05), only with less radiotherapy (39.88% vs. 48.34%, P<0.05). Median follow-up data of 78 months showed that the prognosis of IDC patients was better than that of ASC patients (all P <0.05 for BCSM and OS). After adjustment for clinicopathological and therapeutic factors in Cox proportional hazards models, ASC was no longer an independent poor prognosis factor. In matched groups, no significant difference in BCSM nor OS was observed between ASC and IDC groups. In HR-negative patients, the prognosis of ASC was similar with that of IDC, and both were superior to SCC. In HR-positive patients, the five-year survival rate of ASC was only about 60%, which was far less than that in ASC of HR-negative, the poor prognosis of ASC was closer to that of SCC. Multivariate analysis showed that older age (age≥60) and advanced AJCC stage (III and IV) were independent factors of poor prognosis in ASC, breast-conserving surgery was also ideally suited for ASC. Conclusions: ASC has unique clinicopathological characteristics and prognosis. To improve the clinical and biological understanding of ASC can make breast cancer patients get more individualized treatment.