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TKI Macrocytosis — SCE Medical Oncology MCQ

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EasyImmunotherapy & Targeted TherapyTKI MacrocytosisSCE Medical Oncology

A 62-year-old man on sunitinib for GIST develops progressive fatigue. His FBC shows macrocytic anaemia (MCV 108 fL, Hb 95 g/L). B12 and folate are normal. TSH is normal. What is the likely cause?

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Correct answer: D — Sunitinib-induced macrocytosis — a common class effect of multi-kinase inhibitors affecting erythropoiesis; it is usually clinically insignificant and does not require treatment

Macrocytosis is a very common (up to 70-80%) pharmacological effect of multi-kinase inhibitors (sunitinib, sorafenib, pazopanib). The mechanism is not fully understood but may involve interference with erythropoiesis and folate metabolism through kinase inhibition in haematopoietic precursors. It is usually clinically insignificant (mild-moderate macrocytosis without significant anaemia) and does NOT require B12/folate supplementation. The fatigue is more likely multifactorial (hypothyroidism should always be checked as a concurrent TKI toxicity).

Reference: BNF Sunitinib; ESMO 2024 GIST/Supportive Care; Stein et al Int J Clin Oncol 2012