Background: The nadir value of the absolute neutrophil count (ANC) in the first cycle of chemotherapy is an effective predictor of subsequent neutropenic events. This study was designed to validate an earlier published study based on a retrospective data analysis from a prospective randomized clinical trial.
Methods: The original published model was applied to a trial of 143 patients to cross-validate the model. We also tested the specification of the model on our data by using a logistic regression model with several variables, including first-cycle nadir ANC, age, menopausal status, hormone-receptor status, previous radiotherapy, and first-cycle decrease in hemoglobin concentration. Patients received fluorouracil, doxorubicin, and cyclophosphamide every 21 or 28 days for six cycles without hematopoietic support from colony-stimulating factor.
Results: In the cross-validation analysis, the original model successfully classified patients by risk of neutropenic events (C = 0.78). When the model specification was tested, first-cycle nadir ANC was the sole significant (P < 0.0001) predictor of neutropenic events and the model had a good predictive power (C = 0.78). The estimated relative risk of 4.8 did not differ from the risk cited in the original model (P = 0.91). A significantly higher percentage of our patients with a low first-cycle nadir ANC of 0.25 x 10(9)/liter or less experienced febrile neutropenia (30% versus 10%, P = 0.04) and received at least 85% of the planned dose intensity (55% versus 32%, P = 0.05).
Conclusions: The original risk model used to predict neutropenic events was validated by our study. This information can be used to target high-risk patients for prophylactic treatment with filgrastim (recombinant methionyl human granulocyte colony-stimulating factor) in chemotherapy cycles 2 to 6.