Incidence and survival of patients with T0N1 breast cancers.
56 Background: As imaging modalities have improved, breast cancers are increasingly detected at earlier stages. Patients rarely present with axillary disease but no mammographically evident breast tumor. Based on analysis of Surveillance, Epidemiology and End Results (SEER) data, we determined that there has been an increase in incidence of T1aN1 breast cancers. In response, we hypothesize that T0N1 breast cancer incidence has decreased with increased MRI use. Moreover, SEER analysis showed that T1aN1 patients have worse survival than T1bN1 patients. We thus hypothesize that T0N1 patients have worse survival than T1N1 patients. Methods: We identified 36,093 female patients diagnosed with T0-1 N1 invasive breast cancer from the SEER database. We compared patient and tumor characteristics: age, race, histology, hormone receptor status, and diagnosis year group (1990-1994, 1995-1999, 2000-2005, 2006-2010) – by TN category (T0N1/T1aN1/T1bN1/T1cN1) using chi-square test and ANOVA. Kaplan-Meier method was used to estimate disease specific survival (DSS) for each TN category and diagnosis year group separately. Adjusted hazard ratios were estimated using Cox proportional hazards models. Results: Stage distribution was: T0N1=129, T1aN1=1294, T1bN1=6731, and T1cN1=27942 patients. Median ages were 59.6, 56.3, 59.1, and 58.1, respectively. Time trend analysis of T0N1 cancers showed an increase in incidence from 1990 to 1999 and stability after 2000. Five-year DSS was significantly worse for patients with T0N1 tumors than T1aN1 tumors (84.5% versus 94.1%, HR 0.513, p < 0.0001). T0N1 tumors were more likely to be ER negative than T1b-cN1 tumors (23% versus 16%, p < 0.0001). T0N1 tumors were also more likely to be ER negative than T1aN1 tumors, but did not reach statistical significance (23% vs. 20%, p = 0.09). The proportion of lobular cancers was significantly higher in T0N1 than T1aN1 or T1b-cN1 patients (18% versus 8%, p < 0.0001). Conclusions: Our analysis suggests that T0N1 tumors may differ biologically from T1N1 tumors. Although the incidence of T0N1 tumors did not decrease, it remained stable after 2000 when the use of MRI for occult breast cancers became widely accepted. Our second hypothesis that survival is worse in patients with T0N1 tumors was confirmed by our analysis.