Myelosuppression — Decreased bone marrow activity

Bone marrow tissue contains rapidly proliferating haematopoietic stem cells that constantly replenish the body's peripheral blood supply. Many conventional cytotoxic treatments, including systemic chemotherapy and extensive radiation therapy, work by damaging rapidly dividing cells indiscriminately. Consequently, these therapies inadvertently destroy progenitor cells within the marrow environment, leading to a profound temporary reduction in blood cell manufacture.

Myelosuppression manifests across three primary cellular lineages, either individually or concurrently. Anaemia involves a deficit in red blood cells, reducing systemic oxygenation. Leukopenia, particularly neutropenia, represents a drop in white blood cells, which compromises immune defences and increases vulnerability to severe systemic infections. Finally, thrombocytopenia denotes a deficiency in circulating platelets, elevating the risk of spontaneous haemorrhage, mucosal bleeding, and prolonged bruising.

Myelosuppression is among the most clinically significant and potentially hazardous side effects of cancer treatment. Severe neutropenia can permit mild bacterial infections to escalate rapidly into life-threatening sepsis, requiring immediate hospital admission. Severe thrombocytopenia can cause serious internal or mucosal haemorrhage. Recognising myelosuppression allows oncology teams to adjust treatment schedules, reduce drug dosages, or administer supportive growth factors, ensuring treatments remain safe while keeping patients protected from preventable, life-threatening haematological complications.

Myelosuppression is diagnosed and tracked using routine full blood count (FBC) tests. Key parameters evaluated include the absolute neutrophil count (ANC) to measure infection risk, haemoglobin and haematocrit levels to assess anaemia, and platelet counts to evaluate bleeding risk. Peripheral blood smears may occasionally be examined under microscopy to assess cellular morphology and rule out alternative causes.

Myelosuppression can occur in any patient receiving cytotoxic chemotherapy, extensive radiotherapy, or stem cell transplantation. It is particularly pronounced during treatment for haematological malignancies, including acute myeloid leukaemia, acute lymphoblastic leukaemia, non-Hodgkin lymphoma, and multiple myeloma, but it also regularly affects patients receiving treatment for solid tumours such as breast, lung, ovarian, and gastrointestinal cancers.

Significant myelosuppression often prompts chemotherapy dose reductions, treatment delays, or drug substitutions to allow marrow recovery. Supportive interventions include granulocyte colony-stimulating factors (G-CSF) like filgrastim to accelerate neutrophil recovery, erythropoiesis-stimulating agents or packed red blood cell transfusions for symptomatic anaemia, and prophylactic or therapeutic platelet transfusions to mitigate serious haemorrhagic risks during profound nadirs.