Prognostic risk factors for treatment decision in pT1a,b N0M0 HER2-positive breast cancers

• HER2 overexpression is associated with poor prognosis in breast cancer.
• Trastuzumab (anti-HER2) is effective in treating HER2-positive breast cancer.
• pT1a,b N0M0 breast cancers have an excellent prognosis across all subgroups.
• Prognostic factors in pT1a,b N0M0 HER2-positive breast cancers are lacking.
• The prognostic role of interval cancer detection is suggested.

Although outcomes for women with breast cancers may vary by biologic subtype, patients with T1a,b N0M0 tumors have an excellent prognosis across all subgroups. HER2 overexpression occurs in 15–20% of primary breast tumors, and is associated with diminished disease-free and overall survival. The anti-HER2 monoclonal antibody trastuzumab in combination with chemotherapy is an effective treatment for all stages of HER2 positive breast cancer (bc). However, the absolute benefit decreases as the risk of recurrence lessens and no available randomized adjuvant trial has evaluated the role of trastuzumab in women with pT1a,b N0M0, HER2-positive breast tumors. These findings may explain the debate about the appropriate indication for adjuvant chemotherapy plus trastuzumab in this setting of patients. The aim of this review was to describe known and novel prognostic risk factors to be used for tailored treatment decision in pT1a,b N0M0 HER2-positive tumors. Whether patients with small HER2-positive bc may be suitable for (chemo)therapy reduction strategies, the current available data cannot exclude the need for a more aggressive treatment in a small subset of these subjects. Novel clinical prognostic factors such as interval cancer (IC) detection may help to address this clinically important controversy. A multicenter population-based cancer registry study is currently evaluating whether IC detection may identify patients with pT1a N0M0 HER2-positive tumors in whom the rate of recurrence justifies consideration for use of conventional, trastuzumab-based chemotherapy regimens.