ABSTRACT

Background: Hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-positive breastcancer (BC) is a heterogeneous disease with low pathological complete response (pCR) to standard neoadjuvant treatment. Cyclin-dependent kinase 4 and 6 inhibitors with endocrine and anti-HER2 therapy have shown a potential for chemotherapy omission in this context.
Patients and methods: TOUCH is an international, open-label, phase II trial for postmenopausal patients with cT >1 cm, cN0 or cN1, HR-positive/HER2-positive BC, randomly assigned to 16 weeks of neoadjuvant weekly paclitaxel or palbociclib and letrozole, both with trastuzumab + pertuzumab (HP). The primary objective investigated the interaction between a gene signature of E2F pathway activity (RBsig) and pCR (ypT0N0 or ypTisN0), hypothesizing higher pCR for RBsig-high tumors in the paclitaxel + HP group and for RBsig-low tumors in the palbociclib + letrozole + HP group. RBsig was assessed by RNA-sequencing from pre-treatment biopsies; intrinsic subtypes were
estimated by absolute intrinsic molecular subtyping Treatment-by-biomarker interaction was estimated using logistic regression in 115 assessable patients.
Results: A total of 147 patients were randomly assigned (74 paclitaxel + HP, 73 palbociclib + letrozole + HP) and 145 constituted the treated population, with a median age of 69 years (interquartile range 63-73 years). More patients completed palbociclib versus paclitaxel (94.4% versus 79.5%). The most frequent grade 3-4 adverse events were neutropenia and diarrhea (6.9% versus 43.1% and 11% versus 8.3% in the paclitaxel + HP versus the palbociclib + letrozole + HP groups, respectively). The pCR rate was 32.9% [95% confidence interval (CI) 22.3% to 44.9%] in the paclitaxel + HP group and 33.3% (95% CI 22.7% to 45.4%) in the palbociclib + letrozole + HP group. No significant