Table 1. Characteristics of the study participants (1988–2018)*.
| Women with history of breast cancer | Women with no history of cancer | |||
|---|---|---|---|---|
| No. | % | No. | % | |
| All participants | 57,571 | 100.00 | 230,067 | 100.00 |
| Sociodemographic | ||||
| Age group at index date (years)† | ||||
| 18–34 | 781 | 1.36 | 3,125 | 1.36 |
| 35–44 | 4,768 | 8.28 | 19,059 | 8.28 |
| 45–54 | 13,039 | 22.5 | 52,114 | 22.65 |
| 55–64 | 14,436 | 25.08 | 57,707 | 25.08 |
| 65–74 | 12,361 | 21.47 | 49,395 | 21.47 |
| 75–84 | 8,386 | 14.57 | 33,524 | 14.57 |
| 85+ | 3,800 | 6.60 | 15,143 | 6.58 |
| Calendar period of index date‡ | ||||
| 1988–1994 | 2,656 | 4.61 | 10,619 | 4.62 |
| 1995–1999 | 4,796 | 8.33 | 19,149 | 8.32 |
| 2000–2004 | 11,590 | 20.13 | 46,302 | 20.13 |
| 2005–2009 | 16,381 | 28.45 | 65,480 | 28.46 |
| 2010–2014 | 15,733 | 27.33 | 62,862 | 27.32 |
| 2015–2018 | 6,415 | 11.14 | 25,655 | 11.15 |
| Ethnicity | ||||
| White | 21,187 | 36.80 | 86,187 | 37.46 |
| South Asian | 411 | 0.71 | 2,247 | 0.98 |
| Black | 271 | 0.47 | 1,384 | 0.60 |
| Other and mixed | 221 | 0.38 | 1,228 | 0.53 |
| Unknown | 35,481 | 61.63 | 139,021 | 60.43 |
| Practice postcode quintile of IMD | ||||
| 1 (least deprived) | 11,381 | 19.78 | 45,502 | 19.78 |
| 2 | 9,913 | 17.22 | 39,618 | 17.22 |
| 3 | 11,820 | 20.53 | 47,239 | 20.53 |
| 4 | 11,736 | 20.38 | 46,899 | 20.39 |
| 5 (most deprived) | 12,721 | 22.08 | 50,809 | 22.10 |
| Lifestyle | ||||
| BMI (kg/m2) at index date | ||||
| <18.50 | 908 | 1.58 | 4,561 | 1.98 |
| 18.50–24.99 | 20,958 | 36.40 | 85,030 | 36.96 |
| 25.00–29.99 | 17,565 | 30.51 | 69,052 | 30.01 |
| 30.00–34.99 | 8,666 | 15.05 | 32,401 | 14.08 |
| 35.00–39.99 | 3,302 | 5.74 | 12,549 | 5.45 |
| ≥40.00 | 1,490 | 2.59 | 6,350 | 2.76 |
| Unknown | 4,682 | 8.13 | 20,124 | 8.75 |
| Alcohol intake at index date | ||||
| Never drinker | 7,780 | 13.51 | 35,065 | 15.24 |
| Current drinker | 40,438 | 70.24 | 156,604 | 68.07 |
| Former drinker | 4,436 | 7.71 | 17,181 | 7.47 |
| Unknown | 4,917 | 8.54 | 21,217 | 9.22 |
| Smoking status at index date | ||||
| Nonsmoker | 30,452 | 52.89 | 122,985 | 53.46 |
| Current smoker | 9,565 | 16.61 | 39,986 | 17.38 |
| Former smoker | 16,343 | 28.39 | 60,604 | 26.34 |
| Unknown | 1,211 | 2.10 | 6,492 | 2.82 |
| Comorbidities at index date | ||||
| Diabetes | 3,844 | 6.68 | 14,030 | 6.10 |
| History of coronary heart disease or stroke | 4,648 | 8.07 | 18,523 | 8.05 |
| Prior history of (>1 year before index date)§ | ||||
| Anxiety | 11,986 | 20.82 | 45,482 | 19.77 |
| Depression | 16,771 | 29.13 | 65,628 | 28.53 |
| Cognitive dysfunction¥ | - | - | - | - |
| Fatigue | 11,200 | 19.45 | 42,578 | 18.51 |
| Sleep disorder | 7,221 | 12.55 | 27,528 | 11.97 |
| Opioid prescribing | 12,761 | 22.17 | 47,765 | 20.76 |
| Pain | 44,752 | 77.73 | 173,112 | 75.24 |
| Sexual dysfunction | 1,670 | 2.90 | 6,479 | 2.82 |
| Self-harm | 1,652 | 2.87 | 6,847 | 2.98 |
BMI, body mass index; IMD, Index of Multiple Deprivation.
* Refers to all patients potentially eligible for analyses. The number of patients included in analyses varied by outcome because we excluded women who had that particular outcome in the year before the index date, as we assumed that these were likely to still be under treatment at the index date.
† Women with no history of cancer were individually matched by age (within a 3-year age range) to women in the exposed group.
‡ For women in the exposed cohort, the index date was the date of their cancer diagnosis. Women in the comparison group were matched to exposed women on age and primary care practice and took the same index date as their matched case.
§ Refers to women who had the outcome recorded at >1 year before the index date. Women who had the outcome in the year before the index date were excluded from the cohort.
¥ Patients with a record of cognitive dysfunction at any point prior to the index date were excluded, as changes in cognitive function are often nonreversible.