Adjuvant regimens with trastuzumab administered for small HER2-positive breast cancer in routine clinical practice

Trastuzumab has proven to improve the prognosis of HER2-positive breast cancer, but the information available about its administration for small tumors is still limited. Therefore, we assessed the use of adjuvant regimens with trastuzumab for the treatment of small HER2-positive breast cancer in routine clinical practice.

This observational study was conducted in patients with HER2-positive breast adenocarcinoma ≤1.5 cm who received trastuzumab-based adjuvant treatment in clinical practice. Clinical/histopathological data were retrieved from patients' medical charts.

A total of 101 evaluable patients were enrolled (median age [range], 56.7 [49.0-64.8] years; ECOG 0, 98.0 %; ductal carcinoma, 88.1 %; lymph nodes N0, 79.2 %). Only five (5.0 %) patients received neoadjuvant treatment, while all patients underwent tumor surgery. Adjuvant trastuzumab was administered at a mean (±SD) dose of 5.9 ± 1.5 mg/kg/cycle, and mostly in a three-weekly schedule (89 [89.0 %] patients). The most frequent adjuvant therapy used with trastuzumab was chemotherapy (87 [86.1 %] patients), followed by radiotherapy (63 [62.4 %] patients) and hormone therapy (52 [51.5 %] patients). Chemotherapy regimens mainly included doxorubicin, cyclophosphamide and paclitaxel/docetaxel (n = 30), docetaxel and cyclophosphamide (n = 15), docetaxel and carboplatin (n = 13). Hormone therapy mainly included letrozole (n = 17) and tamoxifen (n = 17). Nine (8.9 %) patients reported trastuzumab-related adverse events; only one allergic reaction reached grade 3 toxicity.

This study shows that trastuzumab-based adjuvant treatment of small HER2-positive breast cancer is mostly based on chemotherapy-mainly paclitaxel/docetaxel. Adjuvant administration of trastuzumab for small HER2-positive breast cancer seems to be similar to that used for larger tumors.