Adults aged ≥80 years (the oldest-old) comprise the fastest growing age group in Western populations. Yet little is known about their cancer burden. In this nationwide study, we assessed their trends in incidence, treatment and survival over a 30-year period, and predicted their future cancer incidence. All 2 468 695 incident cancer cases during 1990 to 2019 were selected from the Netherlands Cancer Registry, of whom 386 611 were diagnosed in the oldest-old (16%). The incidence of the oldest-old was predicted until 2032. Net and overall survival (OS) were calculated. Patients were divided into four age groups (<80, 80-84, 85-89 and ≥90 years). The incidence of the oldest-old doubled between 1990 and 2019 and is expected to grow annually with 5% up to 2032. In virtually all cancers the share of oldest-old patients grew, but declined for prostate cancer (25% in 1990-1994 vs 13% in 2015-2019). The proportion of undetermined disease stage increased with age in most cancers. The application of systemic therapy increased, albeit less pronounced in the oldest-old than their younger counterparts (1990 vs 2019: 12%-34%, 3%-15%, 2%-7% and 1%-3% in <80, 80-84, 85-89 and ≥90 years old). Five-year OS of the oldest-old patients increased by 7 percentage points (to 26%) between 1990 to 1994 and 2015 to 2019 compared to 19 percentage points (to 63%) in <80 years old. The oldest-old cancer patients are a rapidly growing group who benefitted less from improvements in cancer treatment than younger patients, reflecting the multiple challenges faced in the care of the oldest-old.