What are the key investigations to consider when evaluating a patient

Guideline-aligned answer with reasoning, red flags and references. Clinically reviewed by Dr Kola Tytler MBBS CertHE MBA MRCGP.

When evaluating a patient with unexplained weight loss and fatigue for possible malignancy, consider the following investigations:

Offer an urgent chest X-ray (to be done within 2 weeks) to assess for lung or mesothelioma, especially if the patient is over 40 and has symptoms such as fatigue, cough, shortness of breath, or chest pain .
Carry out tests in primary care, including measurement of serum CA125, particularly in women with unexplained weight loss and fatigue, to evaluate for ovarian cancer .
Consider a very urgent full blood count within 48 hours if there is persistent fatigue or unexplained fever, to assess for leukaemia or lymphoma .
In cases with associated abdominal symptoms, offer quantitative faecal immunochemical testing to evaluate for colorectal cancer .

What are the key investigations to consider when evaluating a patient with unexplained weight loss and fatigue for possible malignancy?