Endometriosis, Parity Not Linked in Ca Risk


LYON, FRANCE — The increased risk of cancer seen in patients with endometriosis is unrelated to parity, according to a large study—the first to examine this association.

“We found that contrary to what one might expect, endometriosis and nulliparity did not combine to give a higher cancer risk,” said Dr. Anna-Sofia Mellin, who presented the results at the annual meeting of the European Society for Human Reproduction and Embryology. “We could not show a difference in risk between parous and nonparous women.”

Her study identified 63,630 women, using the National Swedish Inpatient Register, who were discharged from hospital with a diagnosis of endometriosis between 1969 and 2002. From this cohort, 3,822 cancer cases were subsequently identified, using the National Swedish Cancer Register.

The study found no overall increased risk of cancer associated with endometriosis (standardized incidence ratio [SIR] 1.01); however, significantly elevated risks were found for specific cancers such as endocrine tumors (SIR 1.38), ovarian cancer (SIR 1.37), kidney cancer (SIR 1.36), thyroid cancer (SIR 1.33), brain tumors (SIR 1.27), melanoma (SIR 1.23), and breast cancer (SIR 1.08), said Dr. Mellin of the Karolinska Institute in Stockholm.

Endometriosis was associated with a reduced risk of cervical cancer (SIR 0.71).

When parity was considered, no significant differences were noted between parous and nonparous women, although a nonsignificant decrease in ovarian cancer was noted with parity (from SIR 1.48 in nonparous women to SIR 1.3 in parous women).

Most of the increased cancer risk was seen in women with ovarian endometriosis, with only a small but significant increase seen in those with peritoneal endometriosis and no increased risk associated with adenomyosis, she said.

Although the findings are cause for concern, Dr. Mellin said it is too early to recommend that all endometriosis patients receive cancer screening.

“We don't even have any screening for ovarian cancer, so we don't know how to follow these patients. We know that even if you get an ultrasound every year you still get ovarian cancer and it still may have grown too far,” she said in an interview.

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