T1abN0M0 HER2+ invasive breast cancer recurrence: Population-based cohort of 17,000+ consecutive breast cancers 2000-2006 at Kaiser Permanente Northern California (KPNC).

Abstract

551 Background: T1abN0M0 BC has a low recurrence risk. In contrast, HER2+ BC has an increased risk of local/distant recurrence. In small case series of T1abN0M0 HER2+ BCs from tertiary referral centers, recurrence rates have ranged from 8-23%. Data on sites of recurrence have been limited. While adjuvant chemotherapy plus trastuzumab provides a relative reduction in recurrences of ~50% for HER2+ stage II patients, it remains unclear if women with small HER2+ tumors have sufficient risk to warrant such therapy. Methods: All invasive BC diagnosed from 2000 -2006 at KPNC had routine measurement of HER2, ER, PR at a single, high volume laboratory of excellence. A study physician reviewed the medical record of all T1abN0M0 BC to confirm HER2, ER status, stage, therapy, recurrence, and other outcomes. Kaplan-Meier methods were used to estimate recurrence-free (RFI) and distant recurrence-free intervals (DRFI) and 95% confidence intervals (CI). Results: We identified 237 cases of T1abN0M0 HER2+ BC: 116 T1a (including 18 < 0.1 cm) and 121 T1b. Median follow up was 5.8 years. 15 (6.3%) of all T1ab N0 patients had invasive cancer recurrence (ICR) with 7 (2.9%) local only and 8 (3.4%) distant. T1a patients had 3 (2.6%) ICR local only and 1 distant (0.9%) recurrence. 9.1% of T1b patients had ICR: 4 (3.3%) local only and 7 (5.8%) distant. 8 of 11 T1b recurrent patients had 1.0 cm tumors as did 6 of 7 distant T1b recurrences. 3 recurrences were DCIS only. For the T1a and T1b patients, the 5-year RFIs were 96.2% (95% CI 90.0, 98.6) and 91.1% (95% CI 83.4, 95.3); the DRFIs were 99.1% (95% CI 93.9, 99.9) and 94.0% (95% CI 87.1, 97.3) respectively. 24.9% of T1ab patients received adjuvant chemotherapy without a clear benefit. Overall, 8.9% received adjuvant trastuzumab: 3.3% during 2000-2004 and 18.6% during 2005-2006. Conclusions: Recurrence risk for T1a N0 HER2+ BC was too low to justify adjuvant therapy with chemotherapy or trastuzumab. T1b N0 tumors <1.0cm also had very low distant and local recurrence. Nearly half (7/15) of invasive recurrences in T1ab patients were local only and their prevention might be attained with more aggressive local therapy.