Defining safe pre-chemotherapy absolute neutrophil count thresholds in early-stage breast and colon cancer: A real-world retrospective study conducted in a single hospital setting in Saudi Arabia.

Abstract

e12617 Background: A pre-chemotherapy absolute neutrophil count (ANC) threshold of ≥1.5 × 10⁹/L is widely used in clinical practice, despite limited real-world evidence supporting its role in preventing febrile neutropenia (FN), particularly in patients with ethnic neutropenia. In patients with early-stage breast and colon cancer, strict adherence to this cutoff may lead to treatment delays without a clear safety advantage, consistent with previous observations of inferior clinical outcomes among patients with baseline neutropenia. Methods: We conducted a retrospective cohort study of adult patients at a single hospital in Saudi Arabia, predominantly of Arab ethnicity with early-stage breast or colon/rectal cancer who received adjuvant chemotherapy between 2018 and 2025. Patients were grouped according to febrile neutropenia (FN) occurrence and baseline pre-chemotherapy ANC (≥1.5, 1.0–1.49, and < 1.0 × 10⁹/L). FN incidence and relative risk (RR) were assessed overall and stratified by cancer type. Results: The study included 732 patients, of whom 96 (13.1%) developed FN and 636 (86.9%) did not. Among patients without FN, baseline ANC was ≥1.5 ×10⁹/L in 560 patients (88.1%), 1.0–1.49 ×10⁹/L in 60 (9.4%), and < 1.0 ×10⁹/L in 16 (2.5%).Of the 96 FN events, 76 (79.2%) occurred in patients with breast cancer and 20 (20.8%) in those with colon/rectal cancer. Among breast cancer patients who developed FN, ANC was ≥1.5 ×10⁹/L in 62 patients (81.6%), 1.0–1.49 ×10⁹/L in 7 (9.2%), and < 1.0 ×10⁹/L in 7 (9.2%). In colon/rectal cancer patients with FN, ANC was ≥1.5 ×10⁹/L in 14 patients (70.0%) and 1.0–1.49 ×10⁹/L in 6 (30.0%), with no FN events observed at ANC < 1.0 ×10⁹/L.Using ANC ≥1.5 ×10⁹/L as the reference, FN incidence increased from 12.2% to 17.8% and 30.4% at lower ANC categories, corresponding to relative risks of 1.46 and 2.49, respectively. Despite these increases, most FN events across both cancer types occurred in patients with ANC values meeting conventional treatment thresholds. Conclusions: In this real-world cohort of patients with early-stage breast and colon cancer, the majority of febrile neutropenia events occurred despite pre-chemotherapy ANC values considered acceptable for treatment initiation. The risk of febrile neutropenia varied by cancer type and was not consistently predicted by baseline ANC alone. These findings suggest that rigid ANC thresholds may have limited clinical utility and support a more individualized, risk-adapted approach to chemotherapy decision-making. Prospective trials are needed to further define safe pre-chemotherapy ANC thresholds in patients with baseline neutropenia.