The impact of a cancer diagnosis on nonfatal self-injury: a matched cohort study in Ontario

Lena Nguyen; Julie Hallet; Antoine Eskander; Wing C. Chan; Christopher W. Noel; Alyson Mahar; Rinku Sutradhar

doi:10.9778/cmajo.20220157

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Figure 1:
Cohort creation. Note: OHIP = Ontario Health Insurance Plan.
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Figure 2:
Adjusted ratio of relative rates of nonfatal self-injury in patients with cancer compared with controls. Estimates have been adjusted for Elixhauser Comorbidity Index score (dichotomized as low [0–3] or high [≥ 4]).

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Table 1:

Distributions of baseline characteristics among patients with cancer and cancer-free controls

Characteristic	No. (%) of individuals		Standardized difference^*
Characteristic	Cancer-free controls n = 1 607 480	Patients with cancer n = 803 740	Standardized difference^*
Age at diagnosis, yr
18–39	75 689 (4.7)	37 827 (4.7)	0.00
40–49	129 643 (8.1)	64 616 (8.0)
50–59	292 016 (18.2)	146 033 (18.2)
60–69	431 711 (26.9)	215 979 (26.9)
≥ 70	678 421 (42.2)	339 285 (42.2)
Sex
Female	800 122 (49.8)	400 061 (49.8)	0.00
Male	807 358 (50.2)	403 679 (50.2)
Rurality^†
Urban	1 449 450 (90.2)	721 830 (89.8)	0.01
Rural	156 331 (9.7)	81 369 (10.1)
Deprivation quintile^†
Q1 (least)	320 027 (19.9)	160 154 (19.9)	0.00
Q2	319 160 (19.9)	160 118 (19.9)
Q3	315 001 (19.6)	158 534 (19.7)
Q4	319 604 (19.9)	159 311 (19.8)
Q5 (most)	320 046 (19.9)	160 005 (19.9)
Elixhauser Comorbidity Index score
0–3 (low)	1 500 636 (93.4)	727 865 (90.6)	0.10
≥ 4 (high)	106 844 (6.6)	75 875 (9.4)
Prior usage of mental health services
No use of mental health services	991 004 (61.6)	486 962 (60.6)	0.02
Inpatient	13 503 (0.8)	6583 (0.8)
Outpatient	29 524 (1.8)	14 246 (1.8)
Mental health services use	573 449 (35.7)	295 949 (36.8)
Year of diagnosis
2007–2008	–	120 304 (15.0)	NA
2009–2010	–	127 051 (15.8)
2011–2012	–	132 911 (16.5)
2013–2014	–	132 133 (16.4)
2015–2016	–	136 091 (16.9)
2017–2018	–	139 179 (17.3)
2019	–	16 071 (2.0)
Cancer site
Bone sarcoma and PNS	–	1647 (0.2)	NA
Breast	–	112 300 (14.0)
Bronchopulmonary	–	103 831 (12.9)
CNS	–	10 597 (1.3)
Endocrine	–	32 234 (4.0)
Gastrointestinal	–	151 560 (18.8)
Genitourinary	–	169 990 (21.1)
Gynecologic	–	49 417 (6.1)
Hematopoietic and lymphoma	–	92 175 (11.5)
Head and neck	–	19 116 (2.4)
Skin	–	36 748 (4.6)
Other	–	24 125 (3.0)
Cancer stage
0	–	1732 (0.2)	NA
I	–	149 293 (18.6)
II	–	144 163 (17.9)
III	–	93 937 (11.7)
IV	–	107 763 (13.4)
Missing or unknown	–	306 852 (38.2)

Note: CNS = central nervous system, NA = not applicable, PNS = peripheral nervous system.
↵* Imbalance of Elixhauser Comorbidity Index score is indicated by a standardized difference of ≥ 0.10. This covariate was adjusted for in the multivariable model.
↵† The sum of counts does not equal the column total because of individuals with missing information (≤ 1.0%) for this characteristic.

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Table 2:

Difference-in-differences calculation of nonfatal self-injury in the first 5 years after diagnosis

Analysis	Time period	Exposure	N	NFSI frequency	Follow-up time (person-years)	Rate per 10 000 (95% CI)	Difference in rates	Relative rate	Estimates^*
Analysis	Time period	Exposure	N	NFSI frequency	Follow-up time (person-years)	Rate per 10 000 (95% CI)	Difference in rates	Relative rate	DID	Ratio of relative rates^†
Year 0–1 v. 5 year preindex	Pre-index	Cancer	803 740	3704	3 952 538	9.37 (9.07–9.68)	0.73	1.08	–	–
	Pre-index	Controls	1 607 480	6 02	7 870 255	8.64 (8.44–8.85)	0.73	1.08	–	–
	Post-index	Cancer	803 740	716	688 600	10.40 (9.66–11.19)	2.16	1.26	1.43	1.16
	Post-index	Controls	1 607 480	1264	1 534 334	8.24 (7.80–8.71)	2.16	1.26	1.43	1.16
Years 1–5 v. 5 year preindex	Pre-index	Cancer	550 313	2366	2 703 413	8.75 (8.41–9.11)	0.23	1.03	–	–
	Pre-index	Controls	1 100 626	4596	5 394 840	8.52 (8.28–8.77)	0.23	1.03	–	–
	Post-index	Cancer	550 313	1347	1 563 586	8.61 (8.17–9.09)	0.79	1.10	0.56	1.07
	Post-index	Controls	1 100 626	2626	3 356 057	7.82 (7.53–8.13)	0.79	1.10	0.56	1.07
Years 0–5 v. 5 year preindex	Pre-index	Cancer	803 740	3704	3 952 538	9.37 (9.07–9.68)	0.73	1.08	–	–
	Pre-index	Controls	1 607 480	6802	7 870 255	8.64 (8.44–8.85)	0.73	1.08	–	–
	Post-index	Cancer	803 740	2221	2 461 014	9.02 (8.66–9.41)	1.41	1.19	0.68	1.09
	Post-index	Controls	1 607 480	4538	5 960 260	7.61 (7.40–7.84)	1.41	1.19	0.68	1.09

Note: DID = difference in differences (difference in the postindex period – difference in the preindex period), NSFI = nonfatal self-injury.
↵* Unadjusted estimates are presented.
↵† Ratio of relative rates: relative rate in the postindex period / relative rate in the preindex period.