Anaemia is a common complication of malignancy, and can be multifactorial.
- Tumours involving a mucosal or cutaneous surface can bleed, causing loss of haemoglobin
- This can be compounded by reduced coagulation from liver or platelet impairment
- Large tumours may internally haemorrhage
- Replacement of bone marrow by malignant cells
- Effects of cancer treatment on bone marrow
- Suppression of bone marrow function by the products of malignant cells
The last point is the the specific paraneoplastic phenomenen, as the other causes are due to the direct effect of malignant cells or the treatment thereof.
In contrast to the more obvious causes above, anaemia from malignancy due to paraneoplastic phenomenon is more complex.
- Production of amyloid by some malignancies (eg. myeloma) can lead to deposition within the bone marrow and reduction in bone marrow function
- Autoimmune haemolytic anaemia can be induced by any number of malignancies, most commonly haematological. This leads to destruction of red blood cells and anaemia.
- Microangiopathic haemolytic anaemia (MAHA) is uncommon but can occur due to disseminated intravascular coagulation or purpuric haemolytic syndrome.
- Inflammatory cytokines (eg. TNF𝜶) are produced in response to and by many malignancies. These can lead to downregulation of erythropoiesis and anaemia.
- Red cell aplasia is most commonly associated with treatment for malignancies but some (eg. thymoma, haematological) can be the direct cause. This is the result of autoimmune responses against erythrocyte precursors.
Anaemia results in reduced oxygen carrying capacity within the blood. This can lead to fatigue in mild forms, or increased work of breathing or an increase in cardiac output at more severe levels.
Anaemia is defined based on the haemoglobin as:
- Mild (10 - lower limit of normal)
- Moderate (8-10)
- Severe (6.5-8)
- Life threatening (< 6.5)
Anaemia can also impact on the effectiveness of cancer treatment, particularly radiotherapy, due to reduced oxygen levels in the malignant tissues. This leads to a reduction in effectiveness of indirectly acting radiotherapy modalities (photons and electrons) which are in most common use.
Almost any cancer can cause anaemia. Exophytic carcinomas of any surface can bleed; those with large liver metastases can internally haemorrhage, and tumours that replace the bone marrow are often culprits. The haematological malignancies appear to be the most prone to causing paraneoplastic anaemia.
Blood transfusion may be necessary in the short term. The decision on repeatedly transfusing a patient who would otherwise die is complicated and depends on the other factors in the patient's disease such as their potential curability and quality of life.