Endometriosis is a condition where tissue resembling the lining of the uterus, known as the endometrium, grows outside the uterine cavity. This misplaced tissue, while similar, is not cancerous. Despite its benign nature, there is a recognized association between endometriosis and an increased risk of developing certain cancers. This connection is an area of ongoing research, as understanding it can help individuals with endometriosis and their healthcare providers manage potential risks.
Understanding Endometriosis
Endometriosis involves the growth of endometrial-like tissue in locations beyond the uterus, most commonly within the pelvic cavity. These implants frequently appear on the ovaries, fallopian tubes, the outer surface of the uterus, and the lining of the pelvis (peritoneum). Rarely, this tissue can be found in other areas such as the bowel, bladder, or chest.
The misplaced tissue responds to hormonal changes during the menstrual cycle, thickening and bleeding just like the uterine lining. Since this blood has no way to exit the body, it causes inflammation, irritation, and scar tissue formation, which can lead to organs sticking together. Common symptoms include severe pelvic pain, especially during menstrual periods, heavy bleeding, pain during sexual intercourse, and pain with bowel movements or urination. Infertility is also a common concern for individuals with endometriosis.
The Link to Cancer Risk
Endometriosis has been linked to an increased risk of certain types of ovarian cancer. The strongest associations are with clear cell and endometrioid subtypes of ovarian cancer. For clear cell ovarian cancer, the risk can be as high as 3.4 to 5.1 times greater, and for endometrioid ovarian cancer, it can be 2.3 to 3.1 times higher compared to those without the condition.
Risk is elevated when endometriosis involves the ovaries, especially with ovarian cysts called endometriomas. Deep infiltrating endometriosis, where tissue spreads to pelvic organs, also carries a higher risk. While these relative risks appear substantial, the overall lifetime risk of ovarian cancer for any individual remains low; thus, the absolute increase in risk for those with endometriosis is still considered small, typically less than 1%. A rare cancer, endometriosis-associated adenocarcinoma, can also arise directly from endometriotic lesions, often in the ovary or bowel. The link to breast cancer is less clear and conflicting across studies, with some finding no significant association while others suggest a small increased risk, particularly for women diagnosed with endometriosis at age 50 or older.
Potential Mechanisms Behind the Link
One prominent mechanism involves chronic inflammation. The repeated bleeding and irritation from endometriotic implants create a persistent inflammatory environment in the pelvis. This long-term inflammation can lead to cellular damage and genetic alterations, potentially driving cancer development.
Hormonal factors also play a role, as endometriosis is an estrogen-dependent condition. Elevated estrogen levels and altered hormone profiles may promote endometriotic tissue survival and proliferation, contributing to a cellular environment conducive to cancer development. Endometriotic lesions often show reduced responsiveness to progesterone, which normally counteracts estrogen’s effects, further exacerbating this hormonal imbalance.
Genetic and epigenetic changes are also implicated. Specific gene mutations, such as those in ARID1A and PTEN, are frequently found in both endometriosis and associated ovarian cancers, suggesting shared molecular pathways. For example, ARID1A mutations are common in ovarian clear cell and endometrioid carcinomas linked to endometriosis, often leading to a loss of the ARID1A protein, a tumor suppressor. The loss of PTEN expression has also been associated with greater endometriosis disease burden.
Bleeding within endometriotic lesions can lead to iron accumulation and subsequent oxidative stress. This iron overload generates reactive oxygen species, which can damage DNA and promote rapid cellular division, contributing to malignant transformation. This complex interplay of inflammation, hormones, genetic changes, and oxidative stress is believed to facilitate the progression from endometriosis to certain associated cancers.
Screening and Risk Management
For individuals with endometriosis, open communication with healthcare providers and regular check-ups are important for risk management. While no universal cancer screening guidelines exist specifically for endometriosis patients beyond general recommendations, vigilance for new or changing symptoms is advised. Discuss symptoms like unusual bleeding, persistent abdominal pain or swelling, or changes in bowel or bladder habits with a doctor, as these can overlap with gynecological cancer symptoms.
Managing endometriosis symptoms, often through hormonal therapies or surgery, may indirectly influence cancer risk by reducing inflammation and hormonal exposure. For instance, hormonal contraceptives can help regulate hormone cycles, potentially lowering ovarian cancer risk by reducing ovulation. Personalized risk assessment with a healthcare provider is recommended to discuss individual circumstances, especially if there is a family history of cancer or severe forms of endometriosis.