For ReachMD, this is Audio Abstracts. The following episode is brought to you by Hologic.
Breast cancer is the most common malignancy in the world and the leading cause of cancer death in women, with approximately 1.68 million new cases diagnosed each year. In this episode, we’ll review two related publications that examined links between premenopausal use of hormonal intrauterine treatments for menorrhagia and breast cancer incidence rates.
Both retrospective, population-based cohort studies identified women aged 30 to 49 who had used the levonorgestrel-releasing intrauterine system to treat heavy menstrual bleeding between the years of 1994 and 2007 using the Medical Reimbursement Registry of Finland, a national database that tracks all medical purchase and reimbursement data. The identified women were then linked to subsequent cases of cancers diagnosed up until age 55 using the Finnish Cancer Registry, a comprehensive database of all cancer cases in Finland.
The main outcome measure of both studies was the standardized incidence ratio of cancer, which was calculated by dividing the number of observed cancer cases by the number of expected cancer cases among all Finnish women of a similar age during the same time period. The first study examined the incidence of several common cancers, while the follow-up study focused exclusively on ductal and lobular breast cancers, the two most common types of breast cancer. Additional analyses were conducted to examine women who made two or more purchases of the intrauterine system during the study period.
The publications showed the following results:
- The use of the levonorgestrel-releasing intrauterine system to treat menorrhagia during reproductive years was associated with a 7% higher incidence of cancer than the general female population of a similar age.
- Comparably, the observed number of cancer cases was 20% higher among women who made two or more intrauterine system purchases compared with the general female population.
- In examining specific cancers, the incidence of breast cancer was 19% higher in intrauterine treatment users and 40% higher in users who made more than one purchase compared with the general population.
- In contrast, the risk of endometrial adenocarcinoma was lower in all intrauterine system users compared with the general population, and this reduction became more evident with continued use.
- Similarly, treatment users also showed significantly lower rates of ovarian, lung, and pancreatic cancers.
- No differences in incidence ratios between the groups were found for other cancers, including stomach, colon, liver, or brain.
To further deduce the role of hormonal intrauterine systems on breast cancer risk, the follow-up study showed the following results:
- The use of the levonorgestrel-releasing intrauterine system to treat menorrhagia was associated with a 20% increased risk of invasive ductal breast cancer and a 33% increased risk of invasive lobular breast cancer compared with the general female population of a similar age.
- Similarly, users who made two or more purchases had the highest risk and were 37% more likely to be diagnosed with ductal breast cancer, and 73% more likely to be diagnosed with lobular breast cancer than the general female population.
- The increased risk of breast cancer among intrauterine treatment users compared with the general population was more pronounced after the first five years of follow-up, and was slightly higher for localized breast cancers than non-localized breast cancers.
The authors concluded that the use of the levonorgestrel-releasing intrauterine system to treat heavy menstrual bleeding during reproductive years was associated with a lower incidence of endometrial, ovarian, pancreatic, and lung cancers. But most notably, say the authors, these findings suggest a possible causal effect of levonorgestrel on breast cancer promotion. However, though it’s possible that breast cancer growth may stem from extended progestin exposure, the authors note that other potential risk contributors such as estrogen therapy, family history of cancer, and confounding lifestyle factors were not taken into consideration for these studies.
This has been a presentation of Audio Abstracts, brought to you by Hologic.
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