Why was the cohort set up?

The number of cancer survivors is increasing worldwide, largely due to ageing populations, advances in early detection and cancer treatment.1 The 5-year prevalences of cancer survivors in Denmark have increased by almost 200% from 2000 to 2020, and close to 6% of the Danish population have been diagnosed with cancer.2 Extensive research has established that globally, but also in countries with equal and free access to health care, there is social inequality in stage at cancer diagnosis, treatment provided and survival.3 Since the introduction of cancer treatment by surgery, then radiation and later systemic chemotherapy, late effects have been a part of the aftermath accompanying survival. Late effects are defined as physiological and psychological symptoms or disorders which occur during or after end of treatment and which may become long-term or chronic.1 Little is known about social inequality in late effects.

A Danish national study of 458 646 adult cancer survivors showed a significantly increased risk of other diseases in all but one of 11 major diagnostic groups, such as diseases in the nervous system and endocrine, cardiovascular, metabolic and respiratory disorders, for cancer survivors across cancer types up to 17 years after treatment compared with cancer-free individuals. This cohort study included only cancer survivors free of the diseases in the diagnostic group prior to the date of the cancer diagnosis.4 A prospective cohort from the USA of more than 12 000 people observed a 37% higher risk of cardiovascular disease and up to 52% higher risk of heart failure in adult cancer survivors compared with cancer-free individuals, depending on cancer type and treatment.5 Additionally, systematic reviews and meta-analyses found that up to 49% of cancer survivors suffer from fatigue6 and 47% suffer from pain.7 A Danish nationwide study reported that 57% have impaired sex life.8 Furthermore, a systematic review of 20 studies of psychological symptoms among long-term cancer survivors showed that 21% reported having depression,9 and another systematic review of 43 studies on mood disorders among long-term cancer survivors found a prevalence of anxiety of 18%.10 An American population-based cohort study found that 20% of breast cancer survivors have lymphoedema 2 years after diagnosis.11 Late effects comprise several other conditions, including sleep problems, peripheral neuropathy, cognitive impairments, physical limitations, problems with body image, psychological issues and reduced quality of life, as well as familial, financial and employment problems.12,13 Thus, physical, psychological and social complications after cancer and cancer treatment should be considered. Not all late effects can be measured objectively, which makes it crucial to include the patient’s perspective.