This study demonstrates that, as a group, adult siblings of long-term survivors of childhood cancer generally report being psychologically healthy. There are, however, small groups of siblings at risk for psychological distress. Risk factors for sibling psychological distress were found in several survivor variable domains. Psychological distress and adverse self-reported health status among the survivor predicted sibling global distress and depression, respectively, with the former predicting both outcomes and the latter predicting depression. A survivor diagnosis of sarcoma was also associated with a risk for sibling somatization. The relative ages between survivor and sibling were also related to global distress, with elevated risk for siblings younger than the survivor. Survivor male sex was also a risk for sibling depression. Finally, sibling factors that increased risk for psychological distress included sibling age less than 30 years at study entry increasing risk for sibling somatization.
Current psychological distress and self-perceived adverse health status in adult survivors may be salient factors associated with psychological distress in the siblings of these survivors. It is noteworthy that, in addition to the health of the siblings themselves bestowing risk for psychological distress, the current medical and psychological status of their cancer survivor brother or sister may have had salience for adult sibling depression. Given that siblings and their survivors were not assessed simultaneously, and the questionnaires specifically ask about psychological distress over the past 7 days, we cannot be confident that the distress of survivors and siblings co-occurred in time. However, such symptoms in the cancer survivor may lead the sibling to worry about the survivor's well-being and create ongoing sibling psychological distress. It is becoming well known that childhood cancer survivors have elevated rates of early mortality compared to the general population [1
]. Sibling worry that a brother or sister may die is well documented during cancer treatment and for adolescent siblings of cancer survivors [18
]. Long-standing health problems of survivors may continue to fuel such worries and manifest in siblings' distress. For example, Lehna used qualitative methods to record the oral history of a sibling of a long-term survivor [38
]. This sibling noted ongoing worries with respect to the growth and fertility of her sibling who had survived cancer over 10 years previously. Additionally, long-standing health concerns among survivors may continue to strain the family [39
] which in turn can impact the siblings.
Being a sibling of a sarcoma survivor was a factor associated with siblings' increased somatization when compared to siblings of leukemia survivors. Sarcoma survivors report ongoing long-term psychological distress and pain issues [22
]. Somatization with multiple pain sites and other symptoms is commonly found in cohorts of chronic pain patients as well as in their family members [41
]. Coupled with this ongoing pain, treatment of sarcomas often requires intensive chemotherapy, radiation therapy, and surgical therapy, with the latter two imparting risk for untoward effects on the survivor's growing musculoskeletal system. Such visible reminders of the childhood cancer family experience may create risk for somatization in siblings who may then notice and worry about bodily sensations more than otherwise.
Siblings younger than the survivors may have greater risk for psychological distress due to a greater impact of diminished parenting time and attention during the period of their survivor's cancer treatment. Siblings older than the child with cancer may have had greater opportunity to find other support systems (e.g. peers, teachers). Additionally, older siblings may be more able to derive some benefit from being a sibling of a child with cancer, such as post-traumatic growth [5
]. These age differences in responses to the survivorship experience with younger sibling age associated with adverse psychological outcomes also highlight the importance of the developmental context that overshadows the childhood cancer survivorship experiences. For example, diminished parenting time and attention may have a particularly notable impact on the social and emotional development tasks of younger siblings.
Reason for greater depression among siblings of male survivors is unknowable in this cross-sectional study. It could be that females with cancer might provide more support to their siblings than do male survivors, or that male children / adolescents with cancer might be less open and expressive about their feelings during and after treatment that might serve to undermine the survivor-sibling relationship over time. Furthermore, male siblings were less likely to report somatization, a finding that suggests that male siblings may be less focused on bodily symptoms over time and have relative resistance to develop physical manifestations of psychological distress [45
], at least compared to female siblings. There was no significant interactive effect between sibling sex and survivor sex; however, indicating that the impact of sibling gender was independent of their survivor's gender. These age- and gender-specific roles in the long-term survivor-sibling relationship warrant further exploration.
Younger sibling age at baseline assessment was a risk for sibling somatization although the reason for this is not readily apparent in our data. In general, research demonstrates that somatic complaints tend to increase with age. The reason for our finding of increased somatization in younger siblings is interesting. It may be that siblings of cancer survivors may be more focused on physical symptoms as a result of the childhood cancer experience which may result in somatic distress at a younger age. Siblings may also experience memories relating to the cancer experience or may also manifest ongoing fears relating to risk of late effects or recurrence which may result in somatic distress at a younger age.
This study is a cross-sectional secondary data analysis from a retrospective cohort of siblings ascertained through childhood cancer survivors diagnosed between 1970 and 1986. Thus, the generalizability of the results needs to be carefully considered given the historical nature of the study design and the specific characteristics of the survivor cohort. Since the 1970s and early 1980s, the prognosis for pediatric cancer patients has continued to improve and the intensity of treatments has, to varying degrees, changed [1
]. While cancer treatments and healthcare practices have evolved, it is unknown if these changes would influence the degree of impact on siblings. That is, whether the patient is being treated with less intensive therapy or receiving a greater amount of care in the outpatient setting, it is still likely that the parents' attention will be focused on the child with cancer and disruption of the pre-diagnosis family dynamic would still result. The demographic and sociodemographic characteristics of the CCSS cohort also need to be considered. Closely related to sociodemographic factors, siblings and survivors also share a common genetic, family, and cultural background that may contribute to some of the shared variance between siblings and their survivor's psychological health. There may also be biases introduced by the fact that not all of the siblings of the randomly selected survivors participated. Some siblings chose not to participate and in the case of multiple siblings only one sibling was selected. Finally, while care must be taken in interpretation of results when multiple comparisons are made, factors remained significant in our final models even after adjusting for multiple comparisons.
Despite these limitations, this is the largest collection of siblings of long-term survivors of childhood cancer that has ever been analyzed. Sibling studies are typically single institution studies often with well under 100 participants and with limited diagnostic representation. The large cohort in the CCSS with 26 participating institutions throughout North America provides the opportunity to study adults who are long-term survivors of childhood cancer, well-characterized through medical record abstraction by diagnosis and treatment. The CCSS also provides a matched cohort of survivors and nearest age adult siblings so that within family sibling-survivor factors can be analyzed for the impact of this early childhood cancer experience on siblings' current psychological health. Furthermore, survivor risk factors and sibling outcomes are measured with validated instruments.