Doublet, triplet and quadruplet regimens
Shorthand for how many active drugs are combined: a doublet is two, a triplet three, a quadruplet four. More drugs usually mean more responses and more side effects, and trials test whether the extra drug earns its place.
Platinum doublets (cisplatin or carboplatin plus a partner) are the chemotherapy standard in lung, bladder and ovarian cancer. FOLFOXIRI is a chemotherapy triplet; quadruplet induction (daratumumab, bortezomib, lenalidomide, dexamethasone) is now standard in myeloma; IO-TKI doublets (pembrolizumab-axitinib) and IO-IO doublets (nivolumab-ipilimumab) compete in kidney cancer; prostate cancer moved from ADT alone to doublets and triplets (ADT + ARPI + docetaxel, PEACE-1, ARASENS). The question in each case is whether the combination beats sequential use of the same drugs, which is rarely tested directly.