Background: Tumor location in the breast varies, with the highest frequency in the upper outer quadrant and lowest frequency in the lower inner quadrant. Nevertheless, tumors in the central and nipple portion (TCNP) are poorly studied types of breast cancer; therefore, we aimed to clarify the clinicopathological characteristics and prognostic features of TCNP. 
Methods: Using the Surveillance, Epidemiology, and End Results database, we identifed 105,037 patients diagnosed with tumor in the breast peripheral quadrant (TBPQ) (n=97,046) or TCNP (n=7,991). The chi-squared test was used to compare categorical variables across TCNP and TBPQ. Cox proportional hazard models with hazard ratios were applied to estimate the factors associated with prognosis.
Results: The median follow-up was over 43 months. Compared with TBPQ, TCNP patients were signifcantly older (age ≥66 years: 40.4% vs 34.1%, P<0.001), with larger tumor sizes (>20 mm size: 46.9% vs 37.3%, P<0.001), higher proportions of TNM stage II–III (18.6% vs 9.9%, P<0.001), and more mastectomies (58.1% vs 37.8%, P<0.001). The breast cancer-specifc survival (BCSS)/overall survival (OS) rate was signifcantly worse for TCNP than for TBPQ. Multivariate Cox analysis showed a higher hazard ratios for TCNP over TBPQ (BCSS: hazard ratios =1.160, P=0.005, 95% CI: 1.046–1.287; OS: hazard ratios =1.301, P<0.001, 95% CI: 1.211–1.398). A subgroup analysis revealed inferior outcomes for TCNP in TNM stage II–III and breast subtype subgroup. Multivariate logistic regression indicated that TCNP was an independent contributing factor to LN metastasis. 
Conclusions: TCNP was associated with older age, larger tumor size, higher TNM stage, and lymph node metastasis. Compared with TBPQ, TCNP had adverse impacts on BCSS and OS.
Keywords: tumor in the central and nipple portion, tumor in the breast peripheral quadrant, prognosis, lymph node metastasis