Why this is correct :

• Metastasis = spread of cancer cells from the primary site to distant organs.
• This is a defining characteristic of malignant tumours.
• Benign tumours do NOT metastasize—they remain localized.

Why the other options are wrong:

• Patients who have undergone surgery are given cannabinoids → Not a standard or universal medical protocol.
• Benign tumours show metastasis → Factually incorrect.
• Heroin accelerates body functions → Incorrect; heroin is a CNS depressant, it slows body functions