Lichen Sclerosus, Breast Cancer, and the Impact of Hormonal Therapy: A Large-Scale Propensity-Matched Retrospective Study
This large-scale propensity-matched retrospective study reveals a bidirectional association where lichen sclerosus is linked to a reduced risk of breast cancer, while breast cancer itself increases the subsequent risk of developing lichen sclerosus through mechanisms likely independent of hormonal therapy.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
The skin on the vulva can develop a chronic, itchy condition called lichen sclerosus, which causes the tissue to become thin, white, and fragile. While the exact cause remains a mystery, doctors have long suspected that low levels of estrogen, the hormone that declines after menopause, play a role in its development. This connection makes sense because the condition is most common in older women. At the same time, breast cancer is a disease where cells in the breast grow out of control, and its risk is often linked to how much estrogen a woman's body has been exposed to over her lifetime. Because both conditions seem tied to the same hormone, researchers have wondered if they are connected. Does having lichen sclerosus change a woman's chances of getting breast cancer? Conversely, does a breast cancer diagnosis, or the treatments used to fight it, change the likelihood of developing lichen sclerosus later?
To answer these questions, a team of researchers from medical centers in the United States and Sweden turned to a massive digital library of medical records. They analyzed data from over 204 million patients across hundreds of healthcare organizations. Instead of looking at small groups, they used a computerized method to match patients with lichen sclerosus to similar women who did not have the condition, ensuring that factors like age, race, and body weight were the same for both groups. They did the same for women with breast cancer, matching them to women who had mammograms but no cancer diagnosis. This allowed them to see if one condition made the other more or less likely to appear in the future, while accounting for the many other things that could influence health.
The study revealed a surprising twist in the relationship between these two conditions. When the researchers looked at women who already had lichen sclerosus, they found that these women were actually less likely to develop breast cancer later in life compared to the matched women without the skin condition. Specifically, about 2.22 percent of the women with lichen sclerosus developed breast cancer, whereas 2.55 percent of the women without it did. This suggests that having the skin condition might offer a slight protective effect against breast cancer, or at least that the two do not travel together as often as some might expect.
The story flips when looking at the reverse direction. The researchers found that women who had already been diagnosed with breast cancer were more likely to develop lichen sclerosus later on compared to women who had never had cancer. Among women with breast cancer who did not receive hormonal treatment, 0.18 percent developed the skin condition, compared to only 0.10 percent of the women without cancer. This indicates that the experience of having breast cancer, or the factors surrounding that diagnosis, increases the risk of developing lichen sclerosus.
A major part of the investigation focused on whether the drugs used to treat breast cancer were to blame. Many breast cancer treatments work by lowering estrogen levels in the body, either by blocking the hormone or stopping the body from making it. Since low estrogen is a suspected cause of lichen sclerosus, it was logical to think these drugs might be the culprit. However, the data told a different story. When the researchers looked at women who received hormonal therapies, such as tamoxifen or aromatase inhibitors, the increase in lichen sclerosus risk was very small and barely noticeable. In fact, the risk of developing the skin condition was highest among women who had breast cancer but did not receive any hormonal treatment at all.
This finding challenges the simple idea that low estrogen is the only reason breast cancer patients get lichen sclerosus. If the drugs were the main cause, the risk should have been highest in the women taking them. Instead, the risk was present even without the drugs, suggesting that something else about having breast cancer—perhaps changes in the immune system or the body's response to the disease itself—might be driving the development of the skin condition. The study also looked at specific types of treatments and found no strong link between any single drug class and a higher risk of the skin condition, with one exception: women receiving a specific type of targeted therapy for a different breast cancer subtype actually had a lower risk of developing lichen sclerosus.
The researchers were careful to note that their study relied on medical codes and records, which means they could not see the severity of symptoms or confirm every diagnosis with a biopsy. They also acknowledged that women with cancer see doctors more often, which might make it more likely for a skin condition to be spotted and recorded. Despite these limitations, the sheer size of the study and the consistency of the results across different groups of patients make the findings robust. The data suggests that while the two conditions are linked, the connection is not a simple cause-and-effect relationship driven solely by hormone levels. Instead, it points to a more complex interaction where the presence of breast cancer itself, or the body's reaction to it, may play a significant role in the development of lichen sclerosus, independent of the treatments used to fight the cancer.
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