An increasing number of patients are living with or surviving cancer due to improvements in detection and treatment. However, patients who survive cancer may experience functional disabilities that impact on health, quality of life and ability to work. For example, physical disorders may include fatigue, reduced muscle strength, cognitive dysfunction, paresthesia or nutrition problems, while mental symptoms may include anxiety, depression, fear of relapse or insomnia. Multidimensional oncological rehabilitation programs have been developed to address these disabilities and to help cancer patients and long-term survivors to reduce morbidity and to improve quality of life. There has been evidence showing that multidisciplinary oncological rehabilitation interventions involving physical, psycho-educational and vocational components led to a better quality of life and a higher rate of return to work than just usual care. In Germany, oncological rehabilitation is an integral part of the healthcare system and part of a modern cancer treatment that immediately follows operation, medical treatment or radiotherapy. Furthermore, it can be used if functional disabilities still remain years after cancer treatment. This review describes the German history and legal basis of oncological rehabilitation as well as the contents of and the evidence for this comprehensive and interdisciplinary treatment.
The Imperial Act (‘Reichsgesetz') on invalidity and old-age insurance, enacted within the framework of the Bismarck social reform in 1891, marked the beginning of the history of medical rehabilitation. In the same century came the sanatoria (from Latin sanare = ‘to heal', ‘to make healthy'), which took up the rehabilitation aspect for treatment of severe diseases such as tuberculosis. At that time the focus of the hospitals was the treatment of curable patients. As a result, the first in-patient facilities were established, which, in addition to acute medical care, also provided rehabilitative measures. The aim of the social policy was the return to work of patients with chronic illness .
Due to the advancement of medicine, in particular in the treatment of tuberculosis, sanatoria became less and less important, resulting in only little progress in the area of rehabilitation between the 2 world wars. However, after the Second World War (WW II) and the Pension Insurance Reorganization Act of 1957, the idea of re-integrating people with illness and disabilities into social life, was reactivated. The focus was primarily on disabled veterans of WW II, whose rehabilitation in the military hospitals was largely based on sporting activities. This, in turn, gave a decisive impetus to sport for the disabled. Reconvalescence treatments - and the health clinics founded in this context - gained in importance and enjoyed extensive financial support. The idea of applying general therapeutic measures, such as for instance cures, not only to re-integrate the needy into the community but also to preserve public health and thus economic productivity, is rooted in particular in the experiences and the suffering of WW II. The concept was first and foremost meant to be a token of appreciation of the post-war generation that had rebuilt Germany, and their achievements. This prevention imperative was valid for 25 years until it was withdrawn in 1984 within the framework of economic savings.
Decreasing financial resources in the social security systems, particularly with health insurance companies and pension insurance institutions, justifiably called the appropriateness and effectiveness of the prophylactic treatment measures into question. Realizing that the well-intentioned expectations ultimately did not justify the financial efforts culminated in a certain disillusionment. Thus, pension insurances established a rehabilitation commission at the end of the 1980s to formulate conceptual proposals for the further development of medical rehabilitation. Instead of promoting the historical spa with its traditional remedies, such as baths, springs, salterns, and high altitudes or seafront locations, the emphasis was put on scientifically based therapies. The Growth and Employment Promotion Act (WFG, ‘Wachstums- und Beschäftigungsförderungsgesetz') of 1997 once again brought about a massive, almost 40% decrease in both applications and approvals for medical rehabilitation services. The WFG was enacted to pursue the objective of reducing rehabilitation costs by 3.7 billion DM, and this against the background of the tense financial situation of the social insurance funds as well as the unfavorable economic situation in Germany. These measures resulted in the first rehabilitation crisis at the end of the 1990s, with the decline of many hospitals and health resorts [2, 3, 4, 5, 6].
However, the idea that people with disability and suffering as a result of diseases and therapies needed care was retained, and medical rehabilitation was not entirely discontinued. It was considered that this approach should be reserved for specific indications such as, for instance, cancer. As a consequence, the years thereafter saw a gradual increase in medical rehabilitation services, which exceeded the 1 million Euro mark at the German Pension Insurance (DRV, ‘Deutsche Rentenversicherung') in 2015 .
Although medical rehabilitation has been and still is affected by considerable financial changes, the original idea and vision - to help people after serious illness and therapy and re-integrate them into social life - were never abandoned. This concept is still unchanged, ranks first as the central task of medical rehabilitation, and is consistently pursued by service providers in the context of rehabilitation.
Today, subsequent rehabilitation (AHB, ‘Anschlussrehabilitation') is part of a modern cancer therapy and normally seamlessly follows acute medical therapy or is used as an intermediate intervention . It is an integral part of our healthcare system and is laid down in the Social Insurance Code (SGB, ‘Sozialgesetzbuch') V (§ 27) relating to health insurance companies as well as in SGB VI (§§ 15 and 31) for the DRV and generally in SGB IX (§ 6). Unlike the case with other indications, spouses of insured persons suffering from cancer, pensioners, or persons already receiving a reduced-earning-capacity pension are entitled to oncological rehabilitation at the expense of the DRV (§ 31 SGB VI). This has historical reasons, but also ensures the high quality standard for the patient specified by the DRV for the implementation of such measures. If the funding from the DRV to health insurance companies for already retired patients or family members with cancer were to change, it would not be possible to sustain this quality standard for all oncological patients in its current form. Thus, in Germany, people in need of rehabilitation enjoy the great and unique benefit that their claim to rehabilitation services is established by law. Nevertheless, the conditions laid down in insurance law, as well as medical conditions, must be met . This situation also has a particular ethical aspect, which at present is not sufficiently recognized by the general population and medical professionals. In other countries, in particular in the Anglo-American states, the social insurance institutions do not offer financed rehabilitation services to people after severe disease and therapy, so that the patients concerned must largely rely on self-help. Germany, however, is committed to paying special consideration, particularly to needy people suffering from long-term consequences after cancer and tumor therapy. In this context, oncological rehabilitation represents an additional and complementary measure in the long-term care of cancer patients.
Application Patterns and Reasons for the Decline
Although the number of approved medical rehabilitation services constantly increased until 2015, a slight but noticeable decrease by up to 5%, depending on the tumor entity, has been observed in the field of oncological rehabilitation since 2011. In 2013, 170,000 patients participated in oncological rehabilitation, but in 2014 and 2015 this figure was only 152,000 and 157,000, respectively. The reasons for the decrease are largely unknown and currently open to much speculation. Scientific activity has been triggered to find an explanation, in particular by the DRV. However, the results of these studies are not yet available. Possible reasons are listed in table 1. In view of the good economic situation in Germany and the almost seamless approval of AHBs by the DRV, it is certainly not clear why patients do not exploit these benefits more. However, before changes can be made in the field of oncological rehabilitation, the outstanding study data will need to be analyzed to respond accordingly .
Contents of Oncological Rehabilitation
The therapeutic approach of oncological rehabilitation results from the long-term consequences of the cancer disease and anti-tumor therapy (table 2). It includes the development of management strategies, but also specific therapeutic procedures. For this, mental as well as physical status of the patient are required. In addition, it is necessary to know the social environment of the person concerned. Other factors also play an important role in the individual development of such management processes and therapies. Performance requirements in professional and everyday life, life circumstances and workplace conditions as well as offers by social security systems deserve particular mention here. Rehabilitation can contribute to enhancing the patient's activities, which may lead to social participation and involvement in working life (fig. 1). Rehabilitation is a multimodal therapy, which includes a wide variety of disciplines [8, 9, 10, 11, 12].
Whereas in Germany, for historical reasons, oncological rehabilitation is provided almost exclusively in hospitals for an average duration of 3 weeks, other countries apply a different approach. Especially in the northern European and Scandinavian countries, oncological rehabilitation is offered in an outpatient setting at specialized centers, accompanying daily life or parallel to occupation, for a longer period of time [13, 14, 15].
Regardless of the method, it is important to ensure that the patient continues to apply the measures learned within the framework of oncological rehabilitation on their own. The term ‘help for self-help' gains a completely new dimension, and describes oncological rehabilitation as a measure very accurately. For the concept to be successful, a comprehensive, interdisciplinary rehabilitation team must be available within the framework of oncological rehabilitation. Only in this way can enhanced training and consultancy services be offered. A 3-week, step-by-step, continuous practical training and theoretical education help familiarize the patient with the important aspects they are supposed to follow independently in the domestic environment. This concerns, for example, the improvement of physical activities, self-treatment of malfunctions relating to the joints, to breathing and incontinence, as well as independent stoma care. In addition, a healthier diet and the optimal food intake, e.g. after surgery of the stomach, pancreas or esophagus, can be learned. Similarly, therapeutic interventions against cytostatics-induced polyneuropathy (CIPN) or cognitive dysfunction can also be learned and applied independently by the patient. Mental suffering, e.g. sleep disorders, depression or anxiety can also be addressed using psycho-oncology advisory services and by learning relaxation techniques or mindfulness exercises. This facilitates transition to an outpatient, long-term psycho-oncological and behavioral-oriented psychotherapy. Moreover, measures targeting integration into working and the social life (e.g. in the form of gradual reintegration), services concerning participation in gainful activity, or consulting on and prescribing of aids and accessories are important elements of oncological rehabilitation .
Evidence in Oncological Rehabilitation
The fact that measures for oncological rehabilitation induce positive effects has been proven using a Cochrane analysis . David Scott and colleagues  analyzed all accessible medical databases for multidimensional rehabilitation programs in adult cancer patients. Their criteria were met by 12 randomized clinical trials which, despite their heterogeneous character, had used the Short-Form (SF-36) questionnaire as an instrument to assess physical and mental health. Compared to a control group, the analysis showed an advantage for the intervention in both physical and mental terms. A meta-analysis demonstrated that physical activity had a significant effect on both the fatigue symptoms and depression and sleep disorders . The short-term effectiveness of inpatient cancer rehabilitation was evaluated in a small sample size longitudinal controlled cohort study with 245 patients in Switzerland. The SF-36, Functional Assessment of Cancer Therapy (FACT) questionnaire and the Hospital Anxiety and Depression Scale (HADS) were used at baseline and at the end of rehabilitation. Moderate but statistically significant improvements in favor of inpatient rehabilitation were observed in quality of life, and physical and mental functioning .
Currently, there is increasing scientific evidence that sports and movement therapeutic measures not only improve physical performance and alleviate psychological complaint symptoms, but can also be considered as adjuvant therapy in the context of a multimodal therapy concept. Several large phase III studies are available, which, using a randomized study design, have shown the efficacy of movement therapy under consideration of other risk factors with regard to patients' survival. Data are particularly supported for patients with breast cancer, colon carcinoma and prostate cancer and can serve as a basis for a therapeutic recommendation [19, 20, 21].
In a study of 573 women with stage I-III colorectal cancer, Meyerhardt et al.  indicated that increased physical activity (> 18 metabolic equivalents (MET)-h per week) reduced cancer-specific mortality by almost 50%. These measures were particularly beneficial in patients who significantly increased their physical activity compared to the initial condition before the oncological disease.
In the Nurse Health Study, Holmes et al.  compared 2,987 women with stage I-III breast cancer according to their different performance levels. In particular, women who engaged in more than 9 MET-h per week had a significant advantage and showed a significant reduction of disease-related mortality.
A retrospective analysis of data from 2,705 men after prostate cancer diagnosis, published in 2011 from the Health Professionals Follow-Up Study, also showed a significant reduction in overall mortality and disease-specific mortality . Patients engaging in at least 3 h of intensive physical activity per week, had a 61% risk reduction of prostate cancer-specific mortality compared to patients who exercised only 1 h per week. The results of these studies suggest that, by means of regular movement therapeutic measures, a reduction in the probability of relapse and disease-specific mortality can be achieved.
Data are also available on the correlation between body mass index (BMI) and the risk of relapse in breast cancer. An exploratory analysis of the ATAC study showed that women with a BMI of ≥ 30 kg/m2 at disease onset had a significantly higher risk of breast cancer relapse than those with a BMI of < 30 kg/m2. However, an adapted diet does not seem to have a significant effect on breast cancer-specific mortality . Correlations between depressive disorders or anxiety states and mortality after cancer diseases have also been described. An analysis by Chan and colleagues in 2015  showed that a mental alteration after cancer leads to significantly increased mortality rates. The effect becomes increasingly pronounced in the long term, after 5 or more years . These data suggest the need for diagnosing the mental impacts of a tumor disease and tumor therapy, and for creating appropriate therapeutic offers . There are recent evidence-based treatment approaches even for difficult-to-treat long-term function disorders, such as CIPN and cognitive dysfunction [26, 27, 28, 29].
Data from Germany on oncological rehabilitation are limited but show positive effects. These effects can be primarily measured in terms of quality of life, anxiety and depression as well as coping (disease processing) . Improvements can also be proven with regard to physical activity and fitness level. Enhancements were reported both in terms of the basic activities and with regard to the physical training status and overall activities. Even months after the end of oncological rehabilitation, the positive effects were still detectable . In addition, a small, randomized study has shown that an intensified interval training had a significant positive effect on quality of life and on re-integration into working life in women with breast cancer. This kind of exercise also contributed to alleviating the fatigue symptoms . In a recent study on a 1-week interval training at 4 and 8 months after rehabilitation, a significant improvement was observed in the metabolic rate and MET/h compared to the control group. The improvement was still detectable even after 2 years .
An older randomized study investigated the effects of oncological rehabilitation on the physical, emotional, cognitive and role function. It also analyzed how oncological rehabilitation changed the global quality of life and future perspectives. Significant positive effects were recorded in particular with regard to emotional function and quality of life .
In Germany, oncological rehabilitation is an integral part of the treatment of cancer patients. It is most efficient immediately after acute medical treatment or during a therapeutic interruption. Rehabilitation can open up possibilities to patients on how to treat and compensate consequences of cancer diseases and anti-tumor therapy independently in the long term. This involves autonomous action, thus increasing the chance to improve quality of life, reduce mortality and better participate in social and working life. In this sense oncological rehabilitation is also an important therapeutic step for long-term cancer survivors. However, further studies are needed to secure the evidence of oncological rehabilitation in Germany.
All authors declare that they have no conflicts of interest.