Background: The aim of this study is to produce a precision dosing application for clinicians to control neutropenia in prostate cancer patients treated with both docetaxel and G-CSF. Chemotherapy-induced neutropenia (CIN) poses serious harm to patients due to the heightened risk of severe infection. Accordingly, chemotherapy dose is assessed at the beginning of each cycle. The therapeutic window of chemotherapy is determined from population studies, with an individual’s dose often scaled by their body surface area. This leads to a large number of patients being over- or under- dosed. We previously developed an application [1] which uses weekly neutrophil counts from the first cycle of docetaxel treatment to predict the level of neutropoenia in subsequent cycles for a given dose of docetaxel. However, in the original app the administration of G-CSF, used as a prophylactic treatment for neutropenia, was not considered. G-CSF administration lacks standardisation and the COVID-19 pandemic has created a highly risk adverse environment to infections, raising the prospects that a clinician will administer G-CSF. Methods: We adapted and combined representations of endogenous and exogenous G-CSF action on CIN from the literature [2,3,4] to capture the inherent feedback effect of circulating neutrophils on progenitor proliferation as well as the stimulatory action of G-CSF injection on proliferation and maturation of progenitor cells. Using data in the public domain from the comparator arm of a phase III clinical trial for metastatic hormone-resistant prostate cancer (NCT00617669), we identified 134 patients treated with docetaxel with recorded weekly blood tests in the first and second cycle, including 27 also receiving G-CSF. We calibrated individualised patient models against neutrophil counts measured in the first cycle by minimising a Bayesian objective function and evaluated their ability to predict the levels observed in the second cycle. Results: The model was able to capture the main features of endogenous and exogenous G-CSF action on neutrophil count described in the literature, including endogenous-G-CSF-mediated rebound above baseline after chemotherapy-induced depletion [4], rapid rise in neutrophil count following exogenous G-CSF administration [5], as well as reduced chemotherapy-induced depletion and earlier recovery under G-CSF treatment compared to chemotherapy alone [5]. Conclusions: This tool has the potential to help determine how a docetaxel patient may best benefit from G-CSF treatment and/or a change in dose of docetaxel. References:

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