Decreased survival in patients with carcinoma of axillary tail versus upper outer quadrant breast cancers: a SEER population-based study

Background: Carcinoma of the axillary tail of Spence (CATS) is a poorly studied type of breast cancer. The clinicopathological characteristics and prognostic features of CATS are unclear. Methods: Using the Surveillance, Epidemiology, and End Results database, we identified 149,026 patients diagnosed with upper outer quadrant breast cancer (UOBC) (n=146,343) or CATS (n=2,683). The median follow-up was 88 months. The primary and secondary outcomes were breast cancer-specific survival (BCSS) and overall survival. The survival outcomes of UOBC and CATS were compared using competing risks analysis, log-rank test, Cox proportional hazards regression model, and propensity score matching method. Multivariate logistic regression was utilized to present the relationship between CATS and lymph node (LN) metastasis. Results: CATS presented a higher grade, higher negative hormone receptor rate, and more positive nodal metastasis. The 10-year BCSS rate was worse for CATS than for UOBC (85.1% vs 87.3%, P=0.001). The multivariate Cox analysis showed a higher hazard ratio (HR) for CATS over UOBC (BCSS: HR =1.20, P=0.001; overall survival: HR =1.11, P=0.019). The difference in the BCSS was also observed in a 1: 1 matched cohort (BCSS P=0.019). A subgroup analysis revealed the inferior outcomes of CATS in the metastatic LN subgroup and the hormone receptor-negative subgroup. The multivariate logistic regression indicated that CATS is an independent contributing factor to LN metastasis. Conclusion: CATS had distinct clinicopathological characteristics and was more likely associated with LN metastasis. Compared to UOBC, CATS had adverse impacts on BCSS.