The Risk of Cancer and the Role of Parity Among Women With Endometriosis
The Risk of Cancer and the Role of Parity Among Women With Endometriosis
Background: Several epidemiological studies have shown an increased cancer risk among women with endometriosis, especially ovarian cancer. Infertility and nulliparity are also known risk factors for different types of cancer. The aim of this study is to investigate cancer risk among women with endometriosis, stratifying for parity.
Methods: Women discharged from a hospital, with the diagnosis of endometriosis from 1969 to 2002, were identified using the National Swedish Inpatient Register. Data were linked to the National Swedish Cancer Register to identify cases of cancer and to the Swedish Multi-Generation Register to calculate parity and age at first birth. Standardized incidence ratios (SIR) were calculated.
Results: A total of 63 630 women entered the study. To exclude cancers already present at the time of endometriosis diagnosis, the first year of follow-up was excluded, leaving a number of 3822 cases of cancer. There was no increased overall risk of cancer (SIR 1.01) among women with endometriosis. Endometriosis was associated with elevated risks for endocrine tumours (SIR 1.38), ovarian cancer (SIR 1.37), renal cancer (SIR 1.36), thyroid cancer (SIR 1.33), brain tumours (SIR 1.27), malignant melanoma (SIR 1.23) and breast cancer (SIR 1.08), as well as a reduced risk for cervical cancer (SIR 0.71). There were no significant differences between nulliparous and parous women with endometriosis regarding cancer risk for any of the cancer types. There was a non-significant decrease in risk of ovarian cancer with increasing parity for women with endometriosis.
Conculsions: Women with endometriosis have an increased risk for several malignancies. The increased risks do not seem to be related to parity.
Epidemiological studies have recently shown that women with endometriosis have an increased risk of different types of malignancies, especially ovarian cancer and non-Hodgkin's lymphoma (Brinton et al., 1997; Olson et al., 2002; Melin et al., 2006). In fact, several studies have indicated endometriosis as a risk factor for ovarian cancer (Ness et al., 2000, 2002). A co-existence of endometriosis and cancer has been estimated to occur in 0.7-5.0% of all cases of ovarian endometriosis (Erzen and Kovacic, 1998; Ogawa et al., 2000; Nishida et al., 2000; Stern et al., 2001). Various histological and molecular genetic studies have even indicated that endometriosis may transform into cancer (Ogawa et al., 2000; Yoshikawa et al., 2000; Varma et al., 2004).
Women with endometriosis have a well-documented increased risk for infertility, but endometriosis as a cause of infertility has been a focus of controversy (Kennedy et al., 2005). Infertility and nulliparity per se are known risk factors for cancer, above all in the ovaries (Adami et al., 1994; Brinton et al., 2004a, 2005a). In a cohort study on infertility, increased risks of colon cancer, ovarian cancer, thyroid cancer and malignant melanoma were shown for women with endometriosis when compared with the general population (Brinton et al., 2005a). Whether the increased prevalence of infertility in women with endometriosis may explain the increased risk of cancer is not known. Modugno et al. (2004) found that infertility or decreased fertility is not the single reason for the increased risk of ovarian cancer in women with endometriosis.
The aim of this study is to extend our previous epidemiological studies, which showed an increased risk of certain forms of cancer in women with endometriosis, and investigate the impact of parity on this risk.
Abstract and Introduction
Abstract
Background: Several epidemiological studies have shown an increased cancer risk among women with endometriosis, especially ovarian cancer. Infertility and nulliparity are also known risk factors for different types of cancer. The aim of this study is to investigate cancer risk among women with endometriosis, stratifying for parity.
Methods: Women discharged from a hospital, with the diagnosis of endometriosis from 1969 to 2002, were identified using the National Swedish Inpatient Register. Data were linked to the National Swedish Cancer Register to identify cases of cancer and to the Swedish Multi-Generation Register to calculate parity and age at first birth. Standardized incidence ratios (SIR) were calculated.
Results: A total of 63 630 women entered the study. To exclude cancers already present at the time of endometriosis diagnosis, the first year of follow-up was excluded, leaving a number of 3822 cases of cancer. There was no increased overall risk of cancer (SIR 1.01) among women with endometriosis. Endometriosis was associated with elevated risks for endocrine tumours (SIR 1.38), ovarian cancer (SIR 1.37), renal cancer (SIR 1.36), thyroid cancer (SIR 1.33), brain tumours (SIR 1.27), malignant melanoma (SIR 1.23) and breast cancer (SIR 1.08), as well as a reduced risk for cervical cancer (SIR 0.71). There were no significant differences between nulliparous and parous women with endometriosis regarding cancer risk for any of the cancer types. There was a non-significant decrease in risk of ovarian cancer with increasing parity for women with endometriosis.
Conculsions: Women with endometriosis have an increased risk for several malignancies. The increased risks do not seem to be related to parity.
Introduction
Epidemiological studies have recently shown that women with endometriosis have an increased risk of different types of malignancies, especially ovarian cancer and non-Hodgkin's lymphoma (Brinton et al., 1997; Olson et al., 2002; Melin et al., 2006). In fact, several studies have indicated endometriosis as a risk factor for ovarian cancer (Ness et al., 2000, 2002). A co-existence of endometriosis and cancer has been estimated to occur in 0.7-5.0% of all cases of ovarian endometriosis (Erzen and Kovacic, 1998; Ogawa et al., 2000; Nishida et al., 2000; Stern et al., 2001). Various histological and molecular genetic studies have even indicated that endometriosis may transform into cancer (Ogawa et al., 2000; Yoshikawa et al., 2000; Varma et al., 2004).
Women with endometriosis have a well-documented increased risk for infertility, but endometriosis as a cause of infertility has been a focus of controversy (Kennedy et al., 2005). Infertility and nulliparity per se are known risk factors for cancer, above all in the ovaries (Adami et al., 1994; Brinton et al., 2004a, 2005a). In a cohort study on infertility, increased risks of colon cancer, ovarian cancer, thyroid cancer and malignant melanoma were shown for women with endometriosis when compared with the general population (Brinton et al., 2005a). Whether the increased prevalence of infertility in women with endometriosis may explain the increased risk of cancer is not known. Modugno et al. (2004) found that infertility or decreased fertility is not the single reason for the increased risk of ovarian cancer in women with endometriosis.
The aim of this study is to extend our previous epidemiological studies, which showed an increased risk of certain forms of cancer in women with endometriosis, and investigate the impact of parity on this risk.
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