Which investigations are recommended for a patient presenting with unexplained weight loss and fatigue in the context of possible malignancy?

For a patient presenting with unexplained weight loss and fatigue where malignancy is suspected, the following investigations are recommended:

• Urgent chest X-ray within 2 weeks for patients aged 40 and over, especially if they have a history of smoking, asbestos exposure, or symptoms such as cough, shortness of breath, chest pain, or appetite loss, to assess for lung cancer or mesothelioma.
• Quantitative faecal immunochemical testing (FIT) for colorectal cancer in patients aged 40 and over with unexplained weight loss and abdominal pain, or aged 50 and over with rectal bleeding.
• Serum CA125 measurement in women aged 18 and over with unexplained weight loss or fatigue to assess for ovarian cancer.
• Urgent direct access CT scan (within 2 weeks) or ultrasound if CT is unavailable for patients aged 60 and over with new-onset diabetes and weight loss, or with symptoms such as diarrhoea, back pain, abdominal pain, nausea, vomiting, or constipation, to evaluate for pancreatic cancer.
• Very urgent full blood count (within 48 hours) to assess for haematological malignancies such as leukaemia in adults with persistent fatigue or other related symptoms.
• Consider referral via suspected cancer pathway for patients with unexplained lymphadenopathy or splenomegaly, which may indicate lymphoma.

These investigations should be guided by additional symptoms and clinical findings to clarify the most likely cancer type and to determine the urgency of referral or further testing.