(HealthDay News) — For patients with human epidermal growth factor receptor 2-positive (HER2+) breast cancer, distant invasive recurrence is low for T1a tumors and is higher for T1b tumors, especially those with T1b tumors reported at 1.0cm, according to a study published online June 2 in the Journal of Clinical Oncology.

Lou Fehrenbacher, MD, from Kaiser Permanente in Northern California, and colleagues investigated the risk of invasive recurrence among 234 patients with small, node-negative HER2+ breast cancer. Participants with T1a+bN0M0 tumors, identified from a large, integrated health care system, had a median follow-up of 5.8 years.

The researchers identified 15 invasive recurrences, of which 47% were local/regional only. The five-year distant invasive relapse-free interval (RFI) was 98.2% among 171 T1ab patients not treated with adjuvant trastuzumab or chemotherapy; 99.0% for T1a patients; and 97.0% for T1b patients. For T1a, T1b, and T1b tumors reported at 1.0cm, the local/regional plus distant five-year invasive RFI was 97.0, 91.9, and 89.4%, respectively. About one-quarter (24%) of the T1ab cohort comprised T1b tumors reported at 1.0cm, which accounted for 61% of the cohort total tumor volume and three-quarters of distant recurrences (75%). The invasive RFI was lower for T1b 1.0cm tumors (84.5%) than for T1a tumors (97.4%; P=0.009).

“Potential risk differences for T1a and T1b, including the 1.0cm tumors, should be considered when making treatment decisions,” the authors write.

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