Real-world hematologic toxicities in patients > 70 versus < 69 with ER positive metastatic breast cancer on CDK 4/6 inhibitors: Single-institution retrospective study.

Abstract

e13039 Background: Since 2015, CDK4/6 inhibitors (CDKi) have become part of standard of care in the treatment ER-positive, Her2Neu negative of metastatic breast cancer (MBC). Hematologic toxicity from CDKi are common. Pooled analysis of prior randomized trials did not show hematologic toxicity between younger and older adult age groups. We sought to review generalizability of these findings to our community population. Methods: We conducted a retrospective single institution retrospective study on patients who were treated with CDKi from 2015 to 2019. Patients were stratified according to age > 70 years and < 69 years. Data from absolute neutrophil count, hemoglobin and platelet count on Days 1 and 15 of the first 2 cycles were graded for hematologic toxicity according to CTCAE v 5.0. Our primary objective was to assess any difference in grade of hematologic toxicities in the different age groups. Our secondary objective was to analyze the association between hematologic toxicities with the presence or absence of bone metastasis and/or prior chemotherapy exposure. Results: A total of 220 patients were reviewed, 140 were < 69 years and 80 > 70 years. There was no significant effect of time (p = 0.91) with respect to the outcome of hematologic toxicity adjusting for age (p = 0.16). Seventy-seven percent (171/220) of patients had evidence of bone marrow (BM) involvement. There was no significant difference in the grade of any hematologic toxicities over time (p = 0.97) and underlying BM disease (p = 0.20). On the other hand, 50% (111/220) patients had previously received an average of one line of chemotherapy. There was significant positive correlation between lines of therapy and grade of neutropenia (rS= 0.25, p = 0.0028). Overall, the estimated median progression free survival (PFS) was 19.1 months. The median overall survival could not be estimated. Conclusions: Our single institution experience does not show significant hematologic toxicity between patient age groups nor evidence of bone metastasis. However, prior exposure to chemotherapy can have a significant effect in the grade of neutropenia. Our study revealed that there is no difference in PFS according to dosing or age which correlates with current literature.