A diagnosis of cancer can be devastating for both a person and his or her family. Over the past 40 years, the number of individuals in Sweden diagnosed with cancer has more than doubled leaving growing numbers of families coping with the aftermath. Many individuals diagnosed with cancer have young children. Parents with cancer and their spouses often struggle to cope with disease and the demands of parenting simultaneously. In fact, previous research has shown children with a parent who has cancer have a greater risk of behavioral problems or distress than children with two healthy parents.

Whether the stress of having a parent with cancer also affects the children’s physical wellbeing hasn’t been studied much. One concern in particular is whether these children may be at increased risk of injury. Injuries are the most common reason for a child to visit a hospital and in some cases lead to deaths. Children who are not well supervised or whose parents have poor mental health are at increased risk of injury. Coping with cancer and the mental anguish it causes may distract parents and possibly place their children at increased risk of injury.

Based on data from nationwide population and health registers in Sweden, Chen, Regodón Wallin et al. now provide evidence that a child with a parent who has cancer is at a greater risk of injury than a child with two parents who are free of cancer. The analysis also revealed that the risk is particularly great if the parent with cancer also develops mental illness after the cancer diagnosis. The risk of injury is greatest in the first year after the parent’s diagnosis. Fortunately, the elevated risk of injury decreases overtime and is almost non-existing after the third year. The analyses suggest that providing extra support for parents with cancer might help to reduce the risk of injury in their children.

Cancer is not only a leading cause of morbidity and mortality among the affected patients, it is also increasingly recognized as a contributor to ill-health in their significant others (Sjovall et al., 2009; Visser et al., 2004; Kazak et al., 2005; Krauel et al., 2012). In Sweden, the number of newly diagnosed cancer patients has more than doubled during the last forty years and a considerable proportion of these patients are parenting minor children (National Board of Health and Welfare, 2014). A diagnosis of cancer in parents has repeatedly been shown to exert psychological and social stress in their children (Visser et al., 2004). Coping with cancer may affect the parenting of both the ill and well parents, further impacting the behavioral and social adaptability of the children (Faulkner and Davey, 2002). In contrast to the relatively rich literature on behavioral and mental well-being of children living with a parent with cancer, few studies have so far addressed somatic health outcomes among these children. In a recent study, we reported that children of parents with cancer had a higher risk of death, both due to cancer and other causes (Chen et al., 2015).

Injury is the most common cause of hospital care among children and accounts for almost one million child deaths annually worldwide (Peden et al., 2008). Sociodemographic, behavioral and psychosocial factors of both children and their family are known determinants of injuries among children (Horwitz et al., 1988). For example, childhood injury has been associated with male sex, risk-taking behavior, lack of parental supervision as well as poor mental health of the parents (Matheny, 1986; Schwebel et al., 2011; Morrongiello et al., 2006b; Peden et al., 2008; McKinlay et al., 2010). To our knowledge, no study has however specifically addressed the impact of parental cancer diagnosis on the risk of child injury. To this end, we leveraged the nationwide population and health registers in Sweden to explore the association between parental cancer diagnosis and the risk of hospital contact for injury among children.

During the study period, 78,815 children (4%) were exposed to a parental cancer diagnosis. The general characteristics of the exposed children differed slightly from the unexposed children, in terms of larger number of siblings, shorter gestational age, higher proportion of delivery through caesarian section, higher proportions of birth weight <2500 or >4000 grams, higher proportion of maternal smoking in early pregnancy, higher paternal and maternal ages at child's birth, as well as higher educational level of the parents (Table 1).

Primary analysis

During follow-up, 15,377 exposed children (incidence rate: 52 per 1000 person-years) and 548,488 unexposed children (incidence rate: 46 per 1000 person-years) had a first hospital contact for injury. Adjusting for only attained age and sex, the exposed children had a 4% higher rate of hospital contact for injury (hazard ratio [HR], 1.04; 95% confidence interval [CI], 1.02–1.05) than the other children. After adjustment for all covariates, the association became stronger (HR, 1.07 [95% CI 1.05–1.09]) (Table 2). Approximately 17% of hospital contacts among the exposed children occurred during the first year after cancer diagnosis, corresponding to an incidence rate of 60 per 1000 person-years and a HR of 1.27 (95% CI 1.22–1.33). The rate increment decreased during the second and third years, and became null after three years (Table 2).

Table 2

	Any Time After Parental Cancer Diagnosis				First Year After Parental Cancer Diagnosis
Characteristics	No. of Children With a Hospital Contact for Injury	Person-years	HR (95%CI) *	p (Wald Test)	No. of Children With a Hospital Contact for Injury	Person-years	HR (95%CI) *	p (Wald Test)
No parental cancer	548,488	11,879,075	1		548,488	11,879,075	1
Parental cancer	15,377	298,302	1.07 (1.05-1.09)		2,674	44,600	1.27 (1.22-1.33)
Time since cancer diagnosis
≤ 1 year	2,674	44,600	1.27 (1.22-1.33)		—	—	—
>1 and ≤3 years	3,850	74,087	1.10 (1.07-1.14)	<0.001	—	—	—
> 3 years	8,853	179,615	1.01 (0.99-1.03)		—	—	—
Sex of the cancer parent
Male	6,554	126,277	1.08 (1.05-1.11)	0.48	1,166	18,917	1.32 (1.24-1.40)	0.13
Female	8,823	172,026	1.06 (1.04-1.09)		1,508	25,683	1.24 (1.18-1.31)
Tobacco-related cancer †
No	12,008	233,848	1.07 (1.05-1.09)	0.72	2,142	35,080	1.29 (1.24-1.35)	0.13
Yes	3,369	64,454	1.08 (1.04-1.12)		532	9,520	1.20 (1.10-1.31)
Alcohol-related cancer ‡
No	10,464	201,389	1.08 (1.05-1.10)	0.30	1,745	28,525	1.30 (1.24-1.37)	0.16
Yes	4,913	96,913	1.06 (1.02-1.09)		929	16,076	1.23 (1.15-1.31)
Predicted 5-year relative survival rate
< 20% §	931	18,845	1.02 (0.95-1.10)		160	3,041	1.15 (0.98-1.35)
20-80%	7,112	136,080	1.08 (1.06-1.11)	0.21	1,243	20,736	1.27 (1.19-1.35)	0.38
≥ 80% ¶	7,334	143,377	1.06 (1.04-1.09)		1,271	20,824	1.30 (1.23-1.38)
Parental psychiatric comorbidity after cancer diagnosis ‖
No	14,630	285,621	1.06 (1.05-1.08)	0.001	2,611	43,663	1.27 (1.22-1.32)	0.45
Yes	747	12,681	1.21 (1.12-1.31)		63	938	1.41 (1.08-1.85)

1. HR, hazard ratio; CI, confidence interval

2. ^*Adjusted for attained age, sex, number of siblings, gestational age, mode of delivery and birth weight of the child, paternal age at child's birth, maternal age at child's birth, maternal smoking during early pregnancy, and the highest educational level of the parents.

3. ^†Tobacco-related cancers include cancers in lung, oesophagus, larynx, pharynx, mouth, lip, salivary glands, tongue, stomach, urinary bladder, kidney, uterine cervix, colon and pancreas.

4. ^‡Alcohol-related cancers include cancers in liver, oral cavity, pharynx, larynx, oesophagus, colorectum and breast.

5. ^§Including cancers in esophagus, liver, gall bladder, biliary tract, pancreas, lung and stomach.

6. ^¶Including cancers in lip, breast, corpus uteri, testis, skin, thyroid and other endocrine glands, and Hodgkin’s lymphoma.

7. ^‖Including depression, anxiety disorders, stress reaction and adjustment disorder.

The association was not modified by the sex of cancer parent or by the expected survival of cancer; the association did not differ between smoking/alcohol-related cancers and other cancers (Table 2; all p>0.05). However, children whose cancer parent had developed a comorbid psychiatric disorder after diagnosis had a higher rate of childhood injury (HR, 1.21 [95% CI 1.12–1.31], compared with children whose cancer parent had no such disease (HR, 1.06 [95% CI 1.05–1.08]) (p = 0.001). As in the overall analysis, the rate increment in these analyses was more prominent during the first year after diagnosis (Table 2).

The overall association was significantly stronger for boys than for girls (p for interaction, < 0.001) (Table 3). When focusing on the first year following parental cancer, no statistically significant difference was however detected between boys and girls (p = 0.17). Neither the overall association nor the association during the first year after parental cancer was modified otherwise by age at follow-up or number of siblings of the child (Table 3).

Table 3

	No Parental Cancer			Any Time After Parental Cancer Diagnosis				First Year After Parental Cancer Diagnosis
Characteristics of the Child	No. of Children With a Hospital Contact for Injury	Person-years	HR (95%CI)	No. of Children With a Hospital Contact for Injury	Person-years	HR(95%CI)	p for interaction	No. of Children With a Hospital Contact for Injury	Person-years	HR (95%CI)	p for interaction
Sex*
Male	313,806	5,966,451	1	9,088	150,070	1.11 (1.08-1.13)	< 0.001	1,594	22,747	1.30 (1.24-1.37)	0.17
Female	234,682	5,912,624	1	6,289	148,233	1.02 (0.99-1.05)		1,080	21,854	1.23 (1.16-1.31)
Age (years)†
< 3	35,157	876,761	1	103	2,106	1.21 (0.99-1.47)		57	1,155	1.25 (0.96-1.63)
3-5	55,452	1,508,188	1	439	11,775	1.07 (0.97-1.18)		131	3,181	1.19 (1.00-1.42)§
6-11	197,984	4,625,786	1	4,085	88,106	1.08 (1.05-1.12)	0.60	756	14,435	1.24 (1.15-1.34)	0.72
12-15	134,995	2,500,216	1	4,698	83,199	1.08 (1.04-1.11)		777	11,429	1.27 (1.18-1.37)
≥ 15	124,900	2,368,124	1	6,052	113,116	1.06 (1.03-1.09)		953	14,400	1.32 (1.23-1.41)
No. of full and half siblings‡
0	56,174	1,346,435	1	1,143	24,301	1.05 (0.98-1.11)		208	3,759	1.30 (1.13-1.50)
1	229,145	4,982,310	1	5,806	113,772	1.06 (1.04-1.09)	0.13	987	16,907	1.24 (1.16-1.32)	0.74
2	151,985	3,242,395	1	4,356	85,386	1.05 (1.02-1.09)		782	12,748	1.28 (1.19-1.38)
≥ 3	111,184	2,307,935	1	4,072	74,843	1.11 (1.07-1.15)		697	11,187	1.31 (1.21-1.41)

1. HR, hazard ratio; CI, confidence interval

2. *Adjusted for attained age and sex of the child, interaction between sex of the child and cancer of the parents, number of siblings, gestational age, mode of delivery and birth weight of the child, paternal age at child's birth, maternal age at child's birth, maternal smoking during early pregnancy, and the highest educational level of the parents.

3. ^†Adjusted for attained age of the child, interaction between attained age of the child and cancer of the parents, sex, number of siblings, gestational age, mode of delivery and birth weight of the child, paternal age at child's birth, maternal age at child's birth, maternal smoking during early pregnancy, and the highest educational level of the parents.

4. ^‡Adjusted for attained age, sex and number of siblings of the child, interaction between number of siblings of the child and cancer of the parents, gestational age, mode of delivery and birth weight of the child, paternal age at child's birth, maternal age at child's birth, maternal smoking during early pregnancy, and the highest educational level of the parents

5. ^§p = 0.054

Among all hospital contacts, 96% were due to unintentional injuries (HR, 1.07 [95% CI 1.05–1.09]). Parental cancer also tended to be associated with a higher rate of intentional self-harm (HR, 1.09 [95% CI 0.95–1.25]) and undetermined or other injuries (HR, 1.11 [95% CI 0.98–1.26]), but not of assault (HR, 0.99 [95% CI 0.87–1.13]). The associations did not appear to further differ by nature, body region, or mechanism of injury, or by place of injury occurrence, either during the entire follow-up or during the first year after cancer diagnosis (Figure 1).

Figure 1

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Among all events of injury, outpatient visit and hospitalization accounted for 83.5% and 16.5% respectively. Although the positive association was only statistically significant for outpatient visit during the entire follow-up (outpatient visit HR, 1.08 [95% CI 1.06–1.10]; hospitalization HR, 1.03 [95% CI 0.99–1.08]), the association was statistically significant for both hospitalization (HR, 1.18 [95% CI 1.07–1.31]) and outpatient visit (HR, 1.29 [95% CI 1.24–1.35]) during the first year after cancer diagnosis.

In this nationwide register-based study, we found that children having a parent with cancer had a higher rate of hospital contact for injury compared with other children. The rate increment was noted for children of all ages as well as for different kinds of injuries or places of injury occurrence, but was most pronounced immediately after the parent’s cancer diagnosis and among children with previous injuries. Comorbid psychiatric diagnoses after the cancer diagnosis rendered further higher rate increment of childhood injury.

Although it has been suggested that adolescents are most prone to psychosocial problems at the time of stressful life experience, younger children are in greater need of supervision and parenting (Phillips, 2014; Macpherson and Emeleus, 2007a; MacPherson and Emeleus, 2007b). The positive association between parental cancer and hospital contact for injury among children at all ages in the present study may therefore be jointly attributable to both the psychological distress among the children and the potential lack of parental supervision needed for injury prevention (Morrongiello et al., 2006a; Davis Kirsch et al., 2003; Faulkner and Davey, 2002; Asbridge et al., 2014; Bylund Grenklo et al., 2013). It has been debated whether boys and girls are differently affected by parental cancer (Krattenmacher et al., 2012; Visser et al., 2005). Our findings show that overall boys had a more pronounced rate increment than girls for injury. At the same age, boys are on average less mature in terms of social-emotional functioning compared to girls (Visser et al., 2005). However, worth noting is that despite the overall difference, boys and girls had similarly increased rates of injury, during the first year after parental cancer diagnosis.

Parental cancer was associated with a higher rate of injury, regardless of nature, mechanism, body region of the injury, or place of injury occurrence. Although a positive association was mainly noted for unintentional injuries, the lack of statistical significance for intentional injuries might be due to the relatively small number of intentional injuries observed. Interestingly and reassuringly, we found no increased rate of assault-related injuries after parental cancer. The fact that the higher rate of injury was noted not only at home, but also in transportation areas, in sports areas, etc., suggests that efforts in preventing injuries in children living with a parent with cancer should include a larger circle of support.

Children’s adjustment appears to vary at different stages of their parent’s cancer disease (Nelson and While, 2002; Huizinga et al., 2010). Our results showed clearly that children had the highest injury rate increase during the first year after the parent’s cancer diagnosis. This finding corroborates earlier findings in indicating that a cancer diagnosis poses severe psychological distress immediately after the diagnosis, both among the cancer patients and among their children (Fang et al., 2012; Lu et al., 2013; Fall et al., 2009; Huizinga et al., 2010). Previous studies have demonstrated that the well-being of children living with a parent with cancer is largely dependent on the adjustment status of their parents to the cancer (Krattenmacher et al., 2012; Nelson and While, 2002; Thastum et al., 2009; Huizinga et al., 2011). This was supported in our findings that children whose parent was also diagnosed with a psychiatric disorder after cancer diagnosis, appeared to have more pronounced rate increase of injury. Furthermore, among children with higher baseline risk of injury (i.e., children with previous hospital contact for injury), parental cancer was associated with an even more elevated risk for future injuries. These results highlight both a high-risk time window and high-risk groups for potential future interventions. Although the number of children living with a parent of cancer will undoubtedly increase due to the increasing cancer incidence and improving cancer survival, the postponement of childbearing, etc., the proportion of such children is however still small, making dedicated intervention both feasible and viable.

Conflicting results have been reported regarding whether maternal cancer has greater adverse impact on children than paternal cancer (Visser et al., 2005; Compas et al., 1994). In line with our previous finding on child mortality after parental cancer, the present study indicated no difference between maternal and paternal cancer in relation to the consequent risk of childhood injury (Chen et al., 2015). In contrast to previous findings, we found no difference in child injury risk by the severity of parental cancer (Krattenmacher et al., 2012). One potential explanation may be the fact that the severity of cancer does not always positively correlate with the adjustment status of the cancer patients. For example, in a recent large-scale study, it was reported that patients of cancers of relatively better survival (e.g., breast cancer) had the highest prevalence of mental disorders, whereas patients of cancers with much severe prognosis (e.g., pancreatic cancer) had the lowest prevalence (Mehnert et al., 2014).

This study is the first to use a population-based sample to examine the impact of parental cancer on the risk of childhood injury. The major strengths of our study include the nationwide cohort design, using the effective record linkage across the high quality Swedish population and health registers and the prospectively and independently collected information on exposure and outcome. These strengths enhance clearly the validity and generalizability of our findings. Some limitations of our study also deserve consideration. For instance, we had no information on the cohabitation or employment status of the parents. A cancer diagnosis may have considerable impact on the marital relationship and the family's economic status (Wozniak and Izycki, 2014; de Boer et al., 2009) which may in turn trigger additional psychological distress of the parents, leading to suboptimal parenting (Tein et al., 2000; Sallinen et al., 2004). Divorce or separation may further contribute to child injuries due to the departure of one parent from the household or simply a joint custody of the child between the parents. Therefore potential modifying effect of residence status within the family, as well as the cohabitation and employment status of the parents on the studied association deserves further investigation. Residual confounding due to unmeasured or unknown confounders is possible, however, with presumably small impact. In the multivariable models, only adjustment for the age of the child and the parental ages at child’s birth had noticeable impact on the increase in injury risk, whereas adjustment for other covariates including birth characteristics of the child and educational level of the parents, which have previously been suggested to be associated with both injury risk among the children and cancer risk among the parents, had rather negligible impact (data not shown) (Innes and Byers, 2004; Sun et al., 2010; Davey Smith et al., 2007; Beiki et al., 2014; Hemminki and Li, 2003). The facts that the rate increment was mainly noted during the first three years after parental cancer diagnosis but not thereafter, and that the rate increment was independent of number of siblings or whether the cancer is smoking/alcohol-related or not, further alleviated concerns about residual confounding. Misclassification of injuries remains possible as only above 80% of outpatient visits were included in the Patient Register currently (National Board of Health and Welfare, 2009). However, such misclassification is largely administrative and arguably non-differential. Cancer parents with established contact with health care may be more likely to seek medical care for their children’s injury. Yet, the opposite can also be postulated that while coping with this major illness, parents are less likely to seek medical care for minor hassles of their children. Such misclassification, if it exists, should have little impact on inpatient care for injury – a proxy of more severe injury event – and could not explain the largely increased injury rate during the first three years after parental cancer diagnosis whereas not thereafter.

In summary, children with a parent of cancer had a greater rate of hospital contact for injury, especially during the first year after cancer diagnosis. The association was also more pronounced for parental cancer with comorbid psychiatric disorders after the cancer diagnosis and among children with previous injuries.

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   The authors confirm that, for approved reasons, some access restrictions apply to the data underlying the findings. The data used in this study are owned by the Swedish National Board of Health and Welfare and Statistics Sweden. According to Swedish law, the authors are not able to make the dataset publicly available. Any researchers (including international researchers) interested in obtaining the data can do so by the following steps: 1) apply for ethical approval from their local ethical review boards; 2) contact the Swedish National Board of Health and Welfare and/or Statistics Sweden with the ethical approval and make a formal application of use of register data. Contact emails for request of register data: Swedish National Board of Health and Welfare: registerservice@socialstyrelsen.se, Statistics Sweden: Mikrodata.individ@scb.se. Please visit http://www.socialstyrelsen.se/register/bestalladatastatistik/bestallaindividuppgifterforforskningsandamal (the Swedish National Board of Health and Welfare) and http://www.scb.se/sv_/Vara-tjanster/bestalla-mikrodata/ (the Statistics Sweden) for detailed information about how to apply for access to register data for research purposes.

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Author details

1. Ruoqing Chen

   Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden

   Contribution

   RC, Obtained funding, Conception and design, Analysis and interpretation of data, Drafting or revising the article

   Contributed equally with

   Amanda Regodón Wallin

   For correspondence

   ruoqing.chen@ki.se

   Competing interests

   The authors declare that no competing interests exist.

   "This ORCID iD identifies the author of this article:" 0000-0003-4911-3543

2. Amanda Regodón Wallin

   Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden

   Contribution

   ARW, Conception and design, Analysis and interpretation of data, Drafting or revising the article

   Contributed equally with

   Ruoqing Chen

   Competing interests

   The authors declare that no competing interests exist.

3. Arvid Sjölander

   Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden

   Contribution

   AS, Conception and design, Analysis and interpretation of data, Drafting or revising the article

   Competing interests

   The authors declare that no competing interests exist.

4. Unnur Valdimarsdóttir

   1. Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden
   2. Center of Public Health Sciences, Faculty of Medicine, University of Iceland, Reykjavík, Iceland

   Contribution

   UV, Conception and design, Drafting or revising the article

   Competing interests

   The authors declare that no competing interests exist.

5. Weimin Ye

   Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden

   Contribution

   WY, Obtained funding, Conception and design, Acquisition of data, Drafting or revising the article

   Competing interests

   The authors declare that no competing interests exist.

6. Henning Tiemeier

   1. Department of Epidemiology, Erasmus MC University Medical Center, Rotterdam, The Netherlands
   2. Department of Child and Adolescent Psychiatry, Erasmus MC University Medical Center, Rotterdam, The Netherlands

   Contribution

   HT, Conception and design, Drafting or revising the article

   Competing interests

   The authors declare that no competing interests exist.

   "This ORCID iD identifies the author of this article:" 0000-0002-4395-1397

7. Katja Fall

   Clinical Epidemiology and Biostatistics, Faculty of Medicine and Health, Örebro University, Örebro, Sweden

   Contribution

   KF, Conception and design, Drafting or revising the article

   Competing interests

   The authors declare that no competing interests exist.

8. Catarina Almqvist

   1. Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden
   2. Lung and Allergy Unit, Astrid Lindgren Children’s Hospital, Karolinska University Hospital, Stockholm, Sweden

   Contribution

   CA, Obtained funding, Conception and design, Acquisition of data, Drafting or revising the article

   Competing interests

   The authors declare that no competing interests exist.

9. Kamila Czene

   Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden

   Contribution

   KC, Conception and design, Acquisition of data, Drafting or revising the article

   Competing interests

   The authors declare that no competing interests exist.

10. Fang Fang

    Department of Medical Epidemiology and Biostatistics, Karolinska Institutet, Stockholm, Sweden

    Contribution

    FF, Obtained funding, Conception and design, Analysis and interpretation of data, Drafting or revising the article

    Competing interests

    The authors declare that no competing interests exist.

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