Cancer

Normal cells show contact inhibition: contact with other cells stops their uncontrolled growth.
Cancer cells have lost this property. They divide in an uncontrolled manner, form tumours, compete with normal cells for nutrients and spread to other sites (metastasis).
So showing contact inhibition is not a property of cancerous cells.

Radiography uses X-rays and computed tomography (CT) uses X-rays to generate a three-dimensional image of the internal organs; X-rays are ionising radiations and can themselves damage DNA.
Histopathological study (biopsy) requires a piece of the suspected tissue to be cut out, so it is an invasive technique.
MRI uses strong magnetic fields and non-ionising radiations to detect pathological and physiological changes in living tissue accurately.
Since MRI involves neither ionising radiation nor surgery, it is the safest of these.
Hence the safest technique is magnetic resonance imaging (MRI).

Malignant tumours are masses of proliferating neoplastic cells that grow rapidly and invade surrounding tissues; cells sloughed from them reach distant sites through blood and start new tumours. This property, called metastasis, is the most feared property of malignant tumours. So the statement is correct.
Benign tumours normally remain confined to their original location and do not spread to other parts of the body.
The pain killer given to patients after surgery is morphine (an opioid), not cannabinoids.
Heroin is a depressant and slows down body functions.
Hence the correct statement is that malignant tumours may exhibit metastasis.