Bortezomib is an anticancer medication widely used in the treatment of multiple myeloma and mantle cell lymphoma. It belongs to the class of drugs known as proteasome inhibitors and works by blocking the proteasome system responsible for degrading proteins inside cells. This inhibition causes the accumulation of damaged and unwanted proteins, leading to stress and programmed death of cancer cells. Bortezomib helps slow the growth and spread of malignant cells and is often used alone or in combination with other chemotherapy agents. It is administered by intravenous or subcutaneous injection under medical supervision and has significantly improved treatment outcomes, especially in patients with relapsed or resistant blood cancers.