Adding the CDK4/6 inhibitor palbociclib to hormone therapy can slow or stop tumour growth in women with early breast cancer, a study in the Journal of Clinical Oncology has shown (6 December 2018)
The 14-week trial involved 307 postmenopausal women with oestrogen receptor-positive primary breast cancer with a tumour of at least 2cm. Patients were randomly assigned to one of four groups: letrozole alone for 14 weeks, letrozole and palbociclib for 14 weeks, or letrozole or palbociclib alone for two weeks followed by 12 weeks of letrozole and palbociclib.
Biopsies at weeks 2 and 14 showed significant suppression of malignant cell proliferation. At week 14, 90% of those who received palbociclib plus letrozole had complete cell-cycle arrest compared with 59% on letrozole alone.
However, overall tumour volume did not differ between groups, which the authors said could be owing to reduced apoptosis in the palbociclib groups.
They concluded that the addition of palbociclib to letrozole markedly enhanced the suppression of malignant cell proliferation, but did not increase tumour shrinkage.
“Correlating biomarkers of antiproliferative response in the context of a randomised neoadjuvant study will be important in determining which patients may derive the most benefit from CDK4/6 inhibitors in ongoing adjuvant studies in early [breast cancer],” the authors said.
 Johnston S, Puhalla A, Wheatley D et al. Randomized phase II study evaluating palbociclib in addition to letrozole as neoadjuvant therapy in estrogen receptor–positive early breast cancer: PALLET trial. J Clin Oncol 2018; 37(3):178–189. doi: 10.1200/JCO.18.01624