Managing endometriosis to prevent ovarian cancer

Moreover, a significant association between preexisting endometriosis and low-grade serous invasive ovarian cancer (OR, 2.11) was demonstrated, while no association was found between endometriosis and the risk of high-grade serous invasive ovarian cancer (Lancet Oncol. 2012 Apr;13[4]:385-94).

A second recently published report – a meta-analysis of 20 case-control and 15 cohort studies published between 1990 and 2012 and involving more than 444,000 patients – found that endometriosis increased cancer risk in case-control or two-arm cohort studies by 27% (relative risk, 1.265) and by approximately 80% in single-arm cohort studies (standard incidence ratio, 1.797). Endometrioid and clear cell carcinomas were more common in endometriosis-associated ovarian cancer, while serous carcinoma was less frequent (Br J Cancer. 2014 Apr 2;110[7]:1878-90).

Findings of both of these large studies have served to clarify the association between endometriosis and specific histologic subtypes and suggested that there are important differences in the pathogenesis of low-grade and high-grade serous ovarian carcinomas.

Clinical implications

It is not clear what causes malignant transformation or what predisposes some patients with endometriosis to develop ovarian cancer, but the risk likely involves genetic and epigenetic influences as well as immunologic, inflammatory, and hormonal factors.

The molecular profiles of the main two types of ovarian cancer are different: While the majority of high-grade serous ovarian tumors are characterized by TP53 mutations, the low-grade carcinomas are characterized by a variety of mutations, including KRAS, BRAF, ERBB2, CTNNB1, and BCL2 mutations.

There currently are not enough data to recommend genetic screening tests in patients with endometriosis, but our hope is that we eventually will be able to screen for “high-risk” endometriotic lesions by testing for genes specific to various histologic subtypes of low-grade ovarian cancer, or by finding and utilizing other biomarkers.

^{Courtesy of Dr. Farr Nezhat}

Ultrasound view of an endometrioma with a mural nodule.

In the meantime, we believe it is important to more thoroughly treat endometriosis and to identify and follow women with a history of the condition, especially those with a long-standing history, those with a history of endometriosis associated with infertility, and those with ovarian endometrioma. Each of these factors predisposes patients to a higher risk of malignant transformation.

Complete surgical resection of all visible endometriosis is the most effective treatment and will afford the best cancer prevention, even in women who are asymptomatic. In a recent Swedish national registry case-control study, women who underwent radical surgical excision of all visible endometriosis were significantly less likely (OR, 0.30) to develop ovarian cancer (Acta Obstet Gynecol Scand. 2013 May;92[5]:546-54).

Suppressive hormonal therapy is another treatment option for patients with no interest in conceiving. Most large endometriomas are functional ovarian cysts that have been invaded by cortical ovarian endometriosis or by small primary endometriomas (J Reprod Med. 1992 Sep;37[9]:771-6).

While hormonal therapy will not always result in complete regression of endometriotic lesions, it will decrease the recurrence rate of endometriomas and can be considered for long-term prevention of potentially premalignant lesions. It is most effective when it follows surgical excision of endometriomas and associated endometriosis.

A patient who has completed childbearing at the time of surgical resection may be offered bilateral salpingectomy, regardless of menopausal status. Salpingectomy in both average and high-risk populations (e.g., BRCA 1/2 carriers) not only prevents high-grade serous carcinoma by eliminating the site of origin, but also may decrease the risk of endometrioid and clear cell carcinoma by blocking the passageway that enables the flow of endometrium and factors that induce inflammation. It is estimated that the procedure reduces the risk of ovarian cancer by 40%.

Interestingly, tubal ligation has historically been shown to decrease the risk of ovarian cancer, and recent data have shown that the risk of endometrioid and clear cell carcinoma is cut even more than the risk of high-grade serous carcinoma (Int J Epidemiol. 2013 Apr;42[2]:579-89).

^{Courtesy Dr. Farr Nezhat}

MRI view of an endometrioma with a malignant mural nodule.

The Society of Gynecologic Oncology recommends that risk-reducing salpingectomy be considered at the time of hysterectomy or other abdominal or pelvic surgery, and in lieu of tubal ligation. The American College of Obstetricians and Gynecologists similarly has stated that prophylactic salpingectomy may offer clinicians the opportunity to prevent ovarian cancer in their patients. Salpingectomy is an important option for all patients, but is especially important when the fallopian tubes are found to be damaged by endometriosis and/or pelvic inflammatory disease. When imaging studies show that endometriomas are present and resection is not performed, pelvic ultrasound should become part of the patient’s routine examination.