Real-world experience with CDK4-6 inhibition in the old and oldest old with a diagnosis of breast cancer.

This study describes characteristics, toxicity and survival in old patients with HR+/HER2-breast cancer (BC) treated with CDK4/6 inhibitors. Retrospective observational study that included patients ≥ 75 years with HR+/HER2-BC treated with CDK4/6 inhibitors between 2017 and 2021. Patients' general and cancer-related data were collected. Comprehensive Geriatric Assessment scales were gathered. Adverse events reported before each cycle were included. At the end of the follow-up period, mortality was retrospectively registered from medical records. All 19 patients (94.7% women, median age 77.9 ± 10.1) were at risk of frailty (G8 ≤ 14) and malnutrition (MNA-SF ≤ 11). Most were independent (52.7% Lawton ≥ 6), had no cognitive impairment (89.5%, MMSE ≥ 24), poor physical performance (70%, SPPB < 8; 62.5% TUG ≥ 12'') and polypharmacy (72.2%). Almost half had stage IV disease (47.1%). Palbociclib+letrozole was the most frequently prescribed treatment (36.8%). All patients developed some toxicity (94.7% hematologic, 36.8% renal) but except one, grade ≤ 2. Over the 42-month follow-up period, 10 reported progression and 8 died. The median survival time was 19.9 ± 3.4 months. Five months after starting treatment, the probability of survival was 73%. At 30 months, 53% of patients survived. We found a high risk of frailty and drug toxicity in this small sample. Most patients presented hematologic toxicity but to a low degree. The probability of survival increases with treatment.