The multivariate ordered logistic regression analysis performed in this study showed that significant predictors for the development of palbociclib-induced neutropenia included use of statins and BMI. Platelet count at the start of palbociclib was not extracted as a significant variable in multivariate analysis, but the lower the platelet count at the start of palbociclib administration, the more likely neutropenia was to develop. PPI was also not extracted as a significant variable, although combined use of PPI tended to be associated with neutropenia.
When the body fat content is high, anticancer drugs reportedly dissolve in adipose tissue and excretion is thus delayed [10–13]. In this study, BMI was extracted as a significant predictor for the development of palbociclib-induced neutropenia. The ROC curve analysis revealed a BMI cut-off of ≥22.3 kg/m2 for the group likely to develop neutropenia (Grade 4). Clinicians should pay close attention to the onset of neutropenia after palbociclib administration among patients with BMI ≥ 22.3 kg/m2.
As for concomitant pharmacotherapies, statin use was extracted as a significant factor in this study. Concomitant use of statins resulted in a lower risk of neutropenia. This result is consistent with the results of basic research suggesting that statins prevent leukopenia [14]. Hypercholesterolemia has been reported as a risk factor for breast cancer [15], and statins are used for patients with hypercholesterolemia. Statins have also been reported to reduce the risk of breast cancer [16]. The concomitant use of statins and palbociclib might be useful in the treatment of breast cancer, although further verification is needed.
Although not significant, concomitant use of PPIs was suggested to potentially diminish the effect of palbociclib. Previous research has reported that co-administration of PPIs was significantly related to the development of neutropenia [17]. Regarding the relationship between combined use of PPIs and the occurrence of neutropenia, an increase in gastric pH due to the inhibitory effects of PPIs on gastric acid secretion may reduce the absorption of palbociclib [18].
Furthermore, although not significant, low pretreatment platelet count was also suggested as a risk factor for neutropenia. This result is consistent with previous findings [19, 20]. Clinicians thus need to know about the incidence and severity of neutropenia, especially in patients with low platelet counts before palbociclib administration.
Several limitations to the current study need to be considered. First, the retrospective nature of the study may have decreased the validity of the data obtained. Second, since this study was performed at a single institute, prospective multicentre studies are needed to confirm the results.
In conclusion, concomitant use of statins and BMI were identified as significant predictors for the development of palbociclib-induced neutropenia in breast cancer. However, our findings need to be confirmed in further studies. Nevertheless, these results may assist in developing strategies to improve the safety, efficacy, and QOL among patients receiving palbociclib.