“…On occasion, a substitution of drugs has yielded an inferior outcome. This was recognized in the German-Austrian HD-85 study, when an attempt was made to omit procarbazine in their OPPA regimen (oncovin, procarbazine, prednisone, adriamycin) and to substitute methotrexate for procarbazine in patients given COMP (cyclophosphamide, oncovin, methotrexate, prednisone) rather than COPP (cyclophosphamide, oncovin, procarbazine, prednisone) [28,29]. This substitution led to inferior event-free survival and led to the introduction of etoposide in the HD-90 studies [30].…”