Colorectal Cancer Patients: What Do They Die Of?
Colorectal Cancer Patients: What Do They Die Of?
The Swedish Family-Cancer Database was created by linking data from several databases. Data on cancers is from the Swedish Cancer Registry, death causes from the Swedish Cause of Death Register, and data on the familial relationships from the Swedish Multigenerational Register. In addition, the database includes socioeconomic information from national census data. The 2010 update includes Swedish residents born after 1931, together with their biological parents, totalling around 12 million individuals, with over one million cancer diagnoses made until 2008. During the set study time, 1987–2008, death causes were coded using International Classification of Diseases 9 (ICD-9) (1987–1996) or ICD-10 (since 1997). The study population was defined as all individuals born before 1967 and residing in Sweden, totalling 6.13 million individuals, of which 95 000 were CRC patients. CRC patients were defined as those with a diagnosis of CRC as the first invasive cancer, and were identified by ICD-7 codes 153 and 154.0. All other individuals were allocated to the non-CRC cohort. The database includes information on both the underlying cause of death and up to five accompanying causes. Causes of death were assigned into several disease categories. The ICD-codes included in the different categories are discussed below.
A Cox regression model with age as the underlying time scale was used to estimate cause-specific HR, comparing CRC patients with individuals without CRC. Calculations were performed using SAS software (PROC PHREG; SAS V. 9.2). Entry time was January 1987, immigration, or presence at census, whichever occurred first. Censoring events included: December 2008, emigration, absence at census, or death from a cause not included in the chosen disease categories. Individuals who initially were part of the reference group were assigned to the CRC group upon CRC diagnosis. First, HRs were estimated for the underlying causes, the event of interest being dying with a specific condition listed as the underlying cause. Next, the multiple causes of death were also considered. Here, the event of interest was defined as dying with any mention of a specific cause in the death certificate. Thus, calculations on the multiple causes always included the underlying cause. Diseases may have a higher incidence shortly after diagnosis. In order to investigate whether the risk to die from a specific cause was higher shortly after or long after diagnosis, time-dependent analyses were conducted. Separate HRs were calculated for the first 5 years and subsequent years after diagnosis. Furthermore, analyses depending on the anatomical location of the tumour were performed, wherein tumours were classified to proximal (ICD-7 codes 153.0, 153.1), distal (153.2, 153.3) or rectal (154.0). Finally, separate HRs were estimated for men and women. The socioeconomic index (categories 'blue-collar', 'white-collar', 'agriculture', 'professional', 'private', 'other/unknown'), sex, and the geographical region of residence (north, south, big city, unknown) were included as covariates, with individuals grouped according to data from the latest census.
ICD-codes used in the disease categories were the following (ICD-10; −9): myocardial infarction (I21-I22; 410), other coronary heart disease (I20, I23–I25; 411–414), cerebrovascular event (I60–I69; 430–438), arterial disease (I70–I79; 440–448), heart failure (I50; 428), pneumonia (J10–J18; 480–487), chronic lower respiratory disease (J40–J49; 490–496), external causes including subgroups (S00-T98, V01-Y98; 800–900, e800–e999), complications of diagnostic or surgical procedures (Y60–Y84; e870–e879), complications of therapeutic drug or vaccine usage (Y40–Y59; e930–e949), suicide (X60–X84; e950–e959), traffic accident (V01–V99; e800–e848), falls (W00–W19; e880–e888), other heart disease (I30–I49, I52; 420–427), gastrointestinal disease (K00-K93; 520–579), dementia (F00-F03, G30; 290, 331.0), diabetes (E10–E14; 250), complications of heart disease (I51; 429), urinary system disease (N00–N39; 580–599), certain symptoms (R00-R99; 780–799), pulmonary circulation disease (I26–I28, J81; 415–417, 514), nervous system disease (G00–G99, except G30; 320–359, except 331.0), hypertensive disease (I10–I19; 401–405), other bacterial disease (A30–A49; 030–041), psychiatric disease (F04–F99; 291–319), anaemia (D50–D64; 280–285), tumours other than CRC (C00-D48, excluding C18–C20, C77–C80 and C97; 140–239, excluding 153, 154.0, 154.1), CRC (C18–C20; 153, 154.0, 154.1).
Methods
Study Population
The Swedish Family-Cancer Database was created by linking data from several databases. Data on cancers is from the Swedish Cancer Registry, death causes from the Swedish Cause of Death Register, and data on the familial relationships from the Swedish Multigenerational Register. In addition, the database includes socioeconomic information from national census data. The 2010 update includes Swedish residents born after 1931, together with their biological parents, totalling around 12 million individuals, with over one million cancer diagnoses made until 2008. During the set study time, 1987–2008, death causes were coded using International Classification of Diseases 9 (ICD-9) (1987–1996) or ICD-10 (since 1997). The study population was defined as all individuals born before 1967 and residing in Sweden, totalling 6.13 million individuals, of which 95 000 were CRC patients. CRC patients were defined as those with a diagnosis of CRC as the first invasive cancer, and were identified by ICD-7 codes 153 and 154.0. All other individuals were allocated to the non-CRC cohort. The database includes information on both the underlying cause of death and up to five accompanying causes. Causes of death were assigned into several disease categories. The ICD-codes included in the different categories are discussed below.
Statistical Method
A Cox regression model with age as the underlying time scale was used to estimate cause-specific HR, comparing CRC patients with individuals without CRC. Calculations were performed using SAS software (PROC PHREG; SAS V. 9.2). Entry time was January 1987, immigration, or presence at census, whichever occurred first. Censoring events included: December 2008, emigration, absence at census, or death from a cause not included in the chosen disease categories. Individuals who initially were part of the reference group were assigned to the CRC group upon CRC diagnosis. First, HRs were estimated for the underlying causes, the event of interest being dying with a specific condition listed as the underlying cause. Next, the multiple causes of death were also considered. Here, the event of interest was defined as dying with any mention of a specific cause in the death certificate. Thus, calculations on the multiple causes always included the underlying cause. Diseases may have a higher incidence shortly after diagnosis. In order to investigate whether the risk to die from a specific cause was higher shortly after or long after diagnosis, time-dependent analyses were conducted. Separate HRs were calculated for the first 5 years and subsequent years after diagnosis. Furthermore, analyses depending on the anatomical location of the tumour were performed, wherein tumours were classified to proximal (ICD-7 codes 153.0, 153.1), distal (153.2, 153.3) or rectal (154.0). Finally, separate HRs were estimated for men and women. The socioeconomic index (categories 'blue-collar', 'white-collar', 'agriculture', 'professional', 'private', 'other/unknown'), sex, and the geographical region of residence (north, south, big city, unknown) were included as covariates, with individuals grouped according to data from the latest census.
Definitions of Disease Categories
ICD-codes used in the disease categories were the following (ICD-10; −9): myocardial infarction (I21-I22; 410), other coronary heart disease (I20, I23–I25; 411–414), cerebrovascular event (I60–I69; 430–438), arterial disease (I70–I79; 440–448), heart failure (I50; 428), pneumonia (J10–J18; 480–487), chronic lower respiratory disease (J40–J49; 490–496), external causes including subgroups (S00-T98, V01-Y98; 800–900, e800–e999), complications of diagnostic or surgical procedures (Y60–Y84; e870–e879), complications of therapeutic drug or vaccine usage (Y40–Y59; e930–e949), suicide (X60–X84; e950–e959), traffic accident (V01–V99; e800–e848), falls (W00–W19; e880–e888), other heart disease (I30–I49, I52; 420–427), gastrointestinal disease (K00-K93; 520–579), dementia (F00-F03, G30; 290, 331.0), diabetes (E10–E14; 250), complications of heart disease (I51; 429), urinary system disease (N00–N39; 580–599), certain symptoms (R00-R99; 780–799), pulmonary circulation disease (I26–I28, J81; 415–417, 514), nervous system disease (G00–G99, except G30; 320–359, except 331.0), hypertensive disease (I10–I19; 401–405), other bacterial disease (A30–A49; 030–041), psychiatric disease (F04–F99; 291–319), anaemia (D50–D64; 280–285), tumours other than CRC (C00-D48, excluding C18–C20, C77–C80 and C97; 140–239, excluding 153, 154.0, 154.1), CRC (C18–C20; 153, 154.0, 154.1).
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