A literature review of cancer diagnostic tests and treatments in adults with intellectual disability

Introduction

In recent years improvements in cancer care and survival in the general population have been observed Loud & Murphy (2017). Studies have emphasised the importance of regular screening and the role that this plays in the early detection of cancer (Ding et al., 2022; Miller, 2013; Whitaker, 2020). Advancements in treatment options, as well as secondary prevention and early detection, are leading to better outcomes and decreased cancer mortality rates in the general population (Ding et al., 2022; Gini et al., 2020; Jemal et al., 2010). Despite these recent developments in treatment, and the implementation of national cancer screening programmes, large gaps exist in diagnostic and treatment options between people with intellectual disabilities and the general population (Cuypers et al., 2024; Mahar et al., 2024).

Adults with intellectual disabilities have significantly lower rates of routine cancer screening and cancer is often diagnosed at more advanced stages (Horsbøl et al., 2023; Kiani et al., 2014). Some studies specifically highlight gaps that exist in national screening programmes for cancers such as breast, cervical and colorectal (Satgé et al., 2023; Sullivan et al., 2003; Swaine et al., 2014). Evidence in the intellectual disability population points towards factors such as limited screening education, distrust in healthcare providers, and inability to provide consent, leading to limited uptake of available screening programmes and there appear to be misassumptions on women with intellectual disability not requiring cervical screening (Power et al., 2024; Swaine et al., 2014; Weise et al., 2024; Xu et al., 2017). While there are many contributing factors to these inequalities, changes in individuals' health status may go unrecognised for significantly longer because of their intellectual disability (Kiani et al., 2014). In some cases, symptoms suggestive of cancer and cancer itself go undetected, and cancers are identified at a late stage or as a cause of death in individuals with intellectual disabilities (Heslop et al., 2022; Mahar et al., 2024). Communicating symptoms of cancer may be difficult for individuals with an intellectual disability, and those around them may not notice signs of illness, both reasons which may contribute to a late-stage cancer diagnosis (Satgé et al., 2014). Ultimately this phenomenon, known as diagnostic overshadowing, may contribute to a decreased quality of life and the unnecessary progression of cancer, resulting in premature mortality (Mason & Scior, 2004; McMahon et al., 2024).

Although cancer is being diagnosed at more advanced stages in adults with intellectual disabilities, the evidence does not show that diagnosis occurs later in life (Mahar et al., 2024; Satgé et al., 2014). In a study conducted by Satgé and colleagues, the age at which individuals with intellectual disabilities were being diagnosed with cancer was younger than the recommended screening age for the general population with Heslop et al. (2022) and Mahar et al. (2024) reporting similar findings in England and Canada respectively. This may be an indication that adults with intellectual disabilities are developing cancer earlier in adulthood, and screening protocols may need to be tailored to this. Recent evidence has shown that individuals with intellectual disabilities were 1.6 times more likely to be diagnosed with Stage IV breast cancer and 1.44 times more likely to be diagnosed with Stage IV colorectal cancer (Mahar et al., 2024). While the reasons why they are developing late-stage cancer at earlier ages have not yet been established, studies suggest that lowering screening ages for people with intellectual disabilities could be beneficial for earlier diagnosis. The prognosis for cancer patients is dependent on the cancer stage at diagnosis, so a later diagnosis in patients with intellectual disabilities could be a key factor accounting for differences in mortality rates.

There is limited research that focuses on treatment options for individuals with intellectual disabilities diagnosed with cancer. Much of the published evidence are case studies based on one individual's cancer experience with no synthesis of the published evidence available (Brown, 2011; Enomoto et al., 2015). In terms of diagnostic tools, while individuals with intellectual disabilities may utilise the same tools as the general population, tools such as mammography, Papanicolaou tests (pap smears), and testicular examinations, remain under-utilised by the intellectual disability population (Satge et al., 2023). The existing gaps in cancer diagnosis may be from patients not receiving regular screening (Chan et al., 2022; Sullivan et al., 2003).

Although the exploration of treatments in case studies are specific to individual patients, these treatments may set a precedent that tailored treatment plans are required for the specific needs of this vulnerable population (Brown, 2011; Delany et al., 2023; Satgé et al., 2014; Sleijfer et al., 1996). Consequently, the aim of this literature review is to explore and synthesise information relating to cancer diagnostic approaches and treatment options for adults with intellectual disabilities and examine the barriers that prevent adults with intellectual disabilities from accessing both diagnostic tools and treatments.

Methods

This literature review was designed to understand the experiences of adults with intellectual disabilities undergoing cancer diagnostic tests and treatments. Literature reviews provide a thorough critique and examination of all the evidence available on the topic and facilitate a descriptive analysis and meaningful synthesis of the current available research (Colquhoun et al., 2014)

4. Screening process

Figure 1 summarises the screening process in a PRISMA diagram. Two assessors [KS, MD] reviewed each of the articles. A third [LL or MMcM] adjudicated in cases of dispute. The initial search resulted in 10,534 publications with 3,991 duplicates removed. A title and abstract screening of 6,543 articles was completed. Then, 236 articles proceeded to full-text review. Finally, 23 articles were extracted, along with 12 articles from citation searching, resulting in a total of 35 articles for inclusion in the literature review.

Figure 1. PRISMA diagram.

Results

A total of 35 articles were included in the final review. After completing the Braun and Clark thematic analysis, the four overriding themes emerged i.e. Prevention, Education, Adaptation and Autonomy. Some overlap was observed in articles that covered multiple themes (Armin et al., 2022; Brown, 2011; Flynn et al., 2016; Sleijfer et al., 1996; Sullivan et al., 2003). The number of people with intellectual disabilities represented in this review was 97,099. Studies were representative of a worldwide population; USA (n=7), UK (n=6), Canada (n=3), France, Australia and Japan (n=2), and Sweden, Denmark, Taiwan and The Netherlands (n=1). Overall, 14 articles investigated preventative measures of cancer screening, seven articles discussed education on cancer and screening for people with intellectual disabilities, seven articles reviewed cancer treatment options for patients with intellectual disabilities, and three articles discussed patient autonomy, see Table 4 in extended data. A summary of each theme’s results is provided. Screening was addressed in prevention and education. Treatments were covered by adaptation and autonomy.

Discussion

This literature review examines the cancer diagnostic approaches and treatments available for adults with intellectual disability and any barriers or enablers associated with them. Results identified the importance of tailored education and application to cancer screening, diagnosis and treatment, and more involvement of adults with intellectual disability in decisions about their own care, on positive impacts on their cancer outcomes. Unique barriers to screening access were identified.

Cancer is one of the leading causes of death worldwide, but treatments have high success rates if it is diagnosed at an early stage (Bates & Triantafyllopoulou, 2018). By utilising secondary prevention, i.e. cancer screening and regular health checkups to diagnose cancer while it is still asymptomatic, cancer may be diagnosed at an early stage while it is still possible to have positive health outcomes (Ouellette‐Kuntz et al., 2015a). Nevertheless, individuals with intellectual disabilities may be unable to recognise signs and symptoms suggestive of cancer or be able to communicate their symptoms to a caregiver, and the caregiver may be unable to recognise symptoms which could make them more easily overlooked unless regular checks occur (Ouellette‐Kuntz et al., 2015a).

Cancer screening uptake is much lower in patients with intellectual disability than those without. For example, women with intellectual disabilities are five times more likely to never be screened for cancer than the general population and a lower rate of mammograms is observed in women with intellectual disability (Ishimaru et al., 2022; Lai et al., 2014). A Taiwanese study reported that the breast cancer screening rate for women with intellectual disabilities was 4.3% compared to 12% of women in the general population, while pap smear rates were 4.8% compared to 28.8% in the general population (Yen et al., 2014). Similarly, men with intellectual disabilities had lower rates of cancer screening. A Canadian routine data-based study on colorectal cancer (n=807,583) reported that 18.3% of intellectual disability participants received a faecal occult blood test in the previous two years, while 32% were up to date with their colorectal screening, compared to the general population at 26.4% for screening in the last two years and 47.2% for being up to date with their screening (Ouellette-Kuntz et al., 2015b). Although the average lifespan of people with intellectual disability has increased, as theoretically has the risk for cancer developing increased, they are still not receiving equitable screening to the general population (Flynn et al., 2016; Lai et al., 2014; Mahar et al., 2024; Satgé et al., 2014; Wilkinson et al., 2011).

People with intellectual disability may not receive necessary cancer screening due to a unique set of barriers (Bates & Triantafyllopoulou, 2018; Delany et al., 2023; Ouellette-Kuntz et al., 2015b). A key risk factor for cancer is ageing, and screening for cancer detection is recommended at specific ages. Historically, the intellectual disability population had shorter lifespans, and many would not reach the age when preventative measures commenced and therefore were excluded from standard screening (Flynn et al., 2016; Lai et al., 2014; Mahar et al., 2024; Satgé et al., 2014; Wilkinson et al., 2011).

Elevated rates of late diagnosis are reported for people with intellectual disabilities compared to the general population. Studies indicate that patients with intellectual disability were more likely to detect breast, colorectal, and lung cancer at stages III and IV rather than stages I or II (Mahar et al., 2024; Satgé et al., 2023). These late-stage diagnoses of cancers meant that only limited treatments were available, and a high mortality rate occurred. Furthermore, people with intellectual disability have an onset of tumours at earlier ages than that of the general population, so if normal screening timelines are followed it may be too late for a timely diagnosis (Heslop et al., 2022; Mahar et al., 2024).

Living circumstances was another barrier to screening access (Sullivan et al., 2003; Xu et al., 2017). A protective factor was seen for those who resided in a group home or medical facilities, where they were more likely to receive cancer screening due to established policies and procedures (Xu et al., 2017). In contrast, others who lived in institutionalised care facilities may have a higher level of intellectual disability and the facility may have less resources, causing them to be screened less (Armin et al., 2022; Sullivan et al., 2003). Additionally, if a patient lives alone in a rural environment, transportation to screenings may be difficult, often leading to less screening attendance (Yen et al., 2014).

Cognitive deficits associated with intellectual disability may make understanding cancer screening procedures or communicating with relevant specialists more difficult, which can heighten stress and anxiety surrounding procedures, resulting in their cancellation (Bates & Triantafyllopoulou, 2018; Horsbøl et al., 2023; Wilkinson et al., 2011). A need for education on cancer screening was identified as critically important, in regard to enabling a person with an intellectual disability to engage with screening. Many individuals with intellectual disabilities are not educated about the need for cancer screening or the processes involved, and often do not feel prepared to attend screening, which reduces uptake (Wilkinson et al., 2011). A lack of education and preparation has contributed to large gaps in cancer screening (Ishimaru et al., 2022). In a study conducted with females with intellectual disability, patients expressed feelings of confusion, and felt they could not communicate their emotions with their providers and that their doctors did not understand the extent of their confusion (Wilkinson et al., 2011). Furthermore, patients felt they were misinformed or given inadequate information about screening procedures resulting in inadequate preparation. Studies revealed that health professionals should take the time to explain to individuals with intellectual disabilities the specific details of mammograms; where they occur, how long they take and describe the experience using easy-read material (Sullivan et al., 2003; Wilkinson et al., 2011). It was also suggested that doctors provide additional support options such as a video for clarity (Wilkinson et al., 2011).

Studies have used different assessment tools such as the Mammography Preparedness Measure (MPM) to address perceived gaps in knowledge of cancer screening for those with intellectual disabilities (Greenwood et al., 2014; Wang et al., 2015). The MPM is a widely used, validated tool to assess if women are emotionally and physically prepared to undergo a mammogram (Greenwood et al., 2014; Wang et al., 2015). This is not only useful in determining whether individuals warrant education on mammograms but is also used to evaluate the success of various forms of mammography education by performing the MPM before and after the education.

Diverse educational tools were employed to address patients' screening knowledge. In the US, researchers used a DVD of an individual with an intellectual disability who overcame barriers during mammography screening, to reduce feelings of fear, and unpreparedness (Greenwood et al., 2014). The DVD was a successful form of increasing preparation for mammography and highlighted the positive impact of presenting a relatable visual representation. Other tools integrated both breast and cervical cancer knowledge. The ‘Women Be Healthy 2’ was an 11-week programme which provided cervical and breast screening information, as well as preparation for screening (Swaine et al., 2014). Results indicated that ‘Women Be Healthy 2’ was effective in educating women with intellectual disabilities about cancer screening. A study called ‘My Health, My Choice’ also focussed on providing cervical and breast cancer screening education to Native American Women with intellectual disabilities and taught them to be able to identify cancer, and to understand the screening processes, utilising hands-on activities to help the women manage their anxiety (Armin et al., 2022). This program demonstrated an increase in cancer knowledge and screening among participants, demonstrating a link between higher levels of education and higher levels of screening engagement.

Studies also explored education surrounding testicular cancer in individuals with intellectual disabilities. An educational programme about testing testicular cancer awareness was developed which utilised a video, anatomical visual aids, and a computer programme to increase individuals' understanding of cancer, and to help them be able to recognize the signs and symptoms sooner (Wilson et al., 2018). Both the educational programme and the information leaflet were determined to have a positive effect on individuals' knowledge and confidence in performing a testicular self-examination.

While education is an important foundation for supporting patients with intellectual disability, it is crucial that this is provided in conjunction with adaptations for cancer treatments (Armin et al., 2023). Healthcare providers should tailor care to each individual's unique cognitive and emotional needs. A variety of treatments were explored in this review. Chemotherapy is a major treatment of cancer, however because of its strength and negative side effects, providers will not always offer this as an option for patients with intellectual disabilities (Delany et al., 2023). In a case study with a patient with testicular cancer, where it was felt that standard chemotherapy would not be tolerated by the patient, a modified regime resulted in the successful treatment of the cancer and he was able to return to normal daily activities. The study concluded that following evidence-based practice is not always the best route of cancer care for individuals with intellectual disabilities, and that health care providers need to take time to make the necessary adjustments to care. Another example of successful chemotherapy was in a patient with tongue cancer where alternative treatments resulted in the successful eradication of the cancer (Enomoto et al., 2015). These case studies demonstrated that individuals with intellectual disabilities should be considered for chemotherapy treatments, and providers should tailor treatment and care to their specific needs.

Radiation was another integral part of cancer treatment that was successfully adapted and employed in patients with intellectual disabilities. A study reported on the successful effective use of outpatient anaesthesia and delivery of radiation therapy in patients with intellectual disabilities who had early-stage lung cancer, for whom surgery was not an option, where the care team individualised care based on the unique needs of the patients (Gandhidasan et al., 2020). Surgery was another form of cancer treatment explored in individuals with intellectual disabilities. There are ethical debates about men with testicular cancer undergoing radical inguinal orchidectomy for both diagnosis and treatment, but the cure rate can be increased by finding an appropriate balance of therapy (Hafeez et al., 2015). A study evaluating surgery in individuals with severe motor and intellectual disabilities, showed seven patients who had cancer surgery all survived and reported satisfactory outcomes (Ishimaru et al., 2022).

Ethical principles play a large role in the type of cancer treatment that individuals with intellectual disabilities receive. In the case of a patient who received a stem cell transplant, an ethical debate ensued about whether the patients with intellectual disabilities should receive a difficult treatment he did not understand (Brown, 2011). After receiving the treatment, the patient developed complications and died soon after. This case study largely focused on treatment ethics, however this known risky therapy was not proven to be successful because of the complications the patient experienced, independent of the presence of an intellectual disability. Similarly, studies explored debates regarding pain management and prescription drugs being used in the treatment of individuals with intellectual disabilities (Axmon et al., 2018; El-Tallawy et al., 2023; Millard & de Knegt, 2019; Segerlantz et al., 2019). Older adults with cancer and intellectual disabilities were less likely to receive prescription pain medications then their counterparts resulting in the under-management of pain and a reduction in quality of life (Segerlantz et al., 2019).

The ethical debate of treating cancer patients with intellectual disabilities continues into the theme of autonomy. Having an intellectual disability may inhibit an individual's understanding of a plethora of topics which may further alter how decisions are made (Hafeez et al., 2015). Nonetheless, the intellectual disability community has a long history of debating how to handle decision-making and notifying patients with intellectual disabilities of different diagnoses, especially when it comes to cancer, complicated by individual country legal frameworks and capacity (Delany et al., 2023; Kiani et al., 2014; Tuffrey-Wijne et al., 2010). Often people with intellectual disabilities have difficulties being independent and may have carers who have influence over their medical, educational, and financial decisions (Kiani et al., 2014). A lack of truth-telling stems from wanting to protect the patient from excess anxiety and distress, though it may limit the patient’s autonomy. However, a lack of evidence was seen about distress after cancer diagnosis in patients with intellectual disability, implying that these patients should be entitled to honesty when it comes to their care and making medical decisions (Bernal & Tuffrey-Wijne, 2008; Flynn et al., 2016). Furthermore, medical professionals participated in non- “truth-telling” due to feelings of discomfort when working with this population, and they conferred solely with care partners about the patient's condition rather than with the patient themselves (Flynn et al., 2016; Tuffrey-Wijne et al., 2010). Studies also found evidence where carers have asked for the professionals to discuss diagnosis with the patients and the professionals refused. Brown explains an ethical dilemma where a patient who was unable to consent for themselves. The best practice determined by the medical team for the patient was to undergo aggressive treatment despite doubts raised by nursing staff (Brown, 2011). It was reported that the patient passed away from pneumonia within a year of treatment, which brings into question the overall suitability of the treatment. Informed consent is a demonstrated successful consent method for patients with intellectual disabilities and should be used as part of a standard protocol. These findings may serve as a guide for healthcare professionals in providing diagnostic and treatment options, educating their patients, and communicating with patients with intellectual disabilities about their illness.

Notwithstanding these findings, this literature review has several limitations including an over reliance on case studies with the heterogeneity of study designs making synthesis more challenging. Additionally, cancer diagnosis and treatment may have a geographical influence which may impact study findings. Equally, the subjective nature of thematic analysis may affect the interpretation and applicability of findings. Lastly, aged results are reported due to a dearth of recent evidence.

Conclusion

This literature review highlights major differences in treatment and diagnosis needs in cancer patients with intellectual disabilities and their general population peers. Unique barriers to screening including living conditions, age, life span and communication difficulties, contributed to later diagnosis and worse cancer outcomes.

In summary, this literature review shows that people with intellectual disability should be provided with more education on cancer screening and treatment options, should have access to screening at earlier ages, should be provided with more tailored treatment options and their autonomy should be given due consideration.