California Teachers Study

Using data from the Breast Cancer Association Consortium (BCAC), this study investigated the relationship between reproductive factors and different subtypes of breast cancer. Reproductive factors include the age at first period (menarche), age at first birth, and breastfeeding. The research team found that the relationship between reproductive factors and risk of breast cancer varied by breast cancer subtype. For example, women who had given birth (parous women) had a lower risk of luminal A-like, luminal B-like, luminal B-HER2–like, and HER2-enriched–like diseases, but had a higher risk of triple-negative breast cancer.  Read more here.
 

Previous research has shown that women have a higher risk of developing differentiated thyroid cancer than men. Using data from the National Cancer Institute’s (NCI) Cohort Consortium, this 2023 publication examined how reproductive and hormonal factors might affect women's risk of differentiated thyroid cancer. The results from this study suggest that age at menarche (first period), age at menopause, use of hormone therapy, and history of hysterectomy or oophorectomy were all associated with risk of differentiated thyroid cancer.  Read more here.
 

Prior research has shown that women who had a hypertensive disorder during pregnancy have a higher risk of developing cardiovascular disease. This study examined whether women who had a hypertensive disorder during pregnancy also had higher rates of emergency department visits and hospitalizations for cardiovascular issues. The researchers found that within the California Teachers Study, women who had hypertension during pregnancy had more cardiovascular disease−related emergency department visits and hospitalizations than women who did not have hypertension during pregnancy. Read more here.
 

Researchers compiled data from the Epidemiology of Endometrial Cancer Consortium to study the relationship between age at last birth and risk of endometrial cancer. They found that within these studies, risk of endometrial cancer declined with increasing age at last birth.  Read more here.
 

Researchers combined data from the Los Angeles-Shanghai Bladder Cancer Study and the CTS to study the relationship between parity (having children) and bladder cancer risk. Parous women (women who had given birth to children) in these studies had at least 30% reduced risk of developing bladder cancer compared with nulliparous women (women who had never given birth).  Read more here.
 

Compared with CTS participants who had never been pregnant, parous CTS participants had a reduced risk for breast carcinoma in situ (CIS) and invasive breast cancer. The risk reduction grew with an increasing number of full-term pregnancies. The age at which participants had their first-full term pregnancy was also associated with breast cancer risk. Participants whose first full-term pregnancy occurred at age 35 or later had a 115% greater risk for breast CIS and a 27% greater risk for invasive breast cancer than participants whose first full-term pregnancy occurred before age 21.  Read more here. 
 

The parental age at which CTS participants were conceived (i.e. how old a CTS participant’s mother and father where when she was conceived) was associated with that participant’s risk of developing non-Hodgkin lymphoma.  Read more here. 
 

A 2008 study found that there was no statistically significant association between incomplete pregnancy (i.e. miscarriage or abortion) and the risk of breast cancer for California Teachers Study participants.  Read more here. 
 

A 2002 study found that CTS participants had a higher incidence rate of breast, ovarian, and endometrial cancer than comparable California women. These three cancers share several risk factors that may be more common among California female teachers, including low parity, short duration of breastfeeding, and use of postmenopausal hormones.  Read more here.
 

Among younger women (<45 years at baseline), later age at first menstruation (>or=14 years) was associated with an increased risk of thyroid cancer. Risk was also elevated in young women with longer menstrual cycles (>30 days) and whose last pregnancy had ended within five years of cohort enrollment. These results suggest that factors related to delayed puberty may play a role in papillary thyroid cancer risk.  Read more here.
 

Researchers found that menopausal hormonal therapy was not associated with risk of B-cell non-Hodgkin lymphoma among postmenopausal women. Bilateral oophorectomy and hysterectomy were associated with a greater risk of NHL among women who had not used menopausal hormonal therapy.  Read more here.
 

Women with a surgically confirmed endometriosis diagnosis were younger than those with a surgically confirmed adenomyosis diagnosis. Having a mother or sister with endometriosis and never having become pregnant were significantly associated with an increased risk of endometriosis. Having a higher number of children (parity), an early full-term pregnancy, early menarche (<or=10 years of age), obesity, and short menstrual cycles (<or=24 days in length) were significantly associated with an increased risk of adenomyosis.  Read more here.
 

Researchers investigated the effects of surgical menopause through bilateral oophorectomy (removal of both ovaries and fallopian tubes). Having the operation did not increase all-cause, cardiovascular, or cancer mortality.  Read more here.
 

A 2014 study suggested that lifelong high estrogen exposure is associated with a decreased risk in Parkinson’s disease, suggesting that estrogen exposure over a long period of time may be important to Parkinson’s disease reduction.  Read more here.
 

A 2014 study found that the association between SNP rs10235235 (locus CYP3A, chromosome 7q22.1) and breast cancer varied by age at menarche. The modest protective effect of rs10235235 only occurred in women with an older age at menarche (>or=15 years) and was not found for women with an age at menarche of <or=11 years, consistent with the well-documented association between later age at menarche and a reduction in breast cancer risk. This relationship between later menarche and reduced risk can likely be attributed to changes in hormone circulation patterns.  Read more here.
 

A 2014 study found 123 signals at 106 loci associated with age at menarche. These genomic loci include genes that have also been implicated with body mass index and various diseases, including rare disorders of puberty. Loci DLK1-WDR25, MKRN3-MAGEL2, and KCNK9 exhibited parent-of-origin specific associations (for example, a trait that is only influenced by father’s chromosome). Findings suggest that these variants intersect to play a role in coordinating the time of puberty.  Read more here.
 

Researchers examined risk factors of ovarian cancer along with specific ovarian cancer subtypes. Higher parity (number of pregnancies) was strongly associated with decreased risk of endometrioid and clear cell carcinoma. Younger age at menopause, never having had endometriosis, and tubal ligation were associated with decreased endometrioid and clear cell tumor risk. Family history of breast cancer only had modest variation among subtypes. Smoking was associated with an increased risk of mucinous but decreased risk of clear cell tumors.  Read more here.
 

Researchers found that for women with a history of preeclampsia, the T allele of IGF1R variant rs2016347 was associated with a lower risk of breast cancer. This effect was most noticeable for HR+ breast cancer and in women whose age at first birth was younger than 30 years.  Read more here.
 

Researchers combined data from the CTS and the Women’s Contraceptive and Reproductive Experiences (CARE) Study to examine the relationship between oral contraceptive use and breast cancer survival. In this study, oral contraceptive use was not associated with all-cause or breast cancer specific mortality among study participants with invasive breast cancer. Read more here.
 

Using data from multiple studies participating in the Epidemiology of Endometrial Cancer Consortium (E2C2), this study estimated the association between full-term pregnancy and endometrial cancer risk. Researchers found that having a full-term pregnancy was associated with a 41% reduction in risk of endometrial cancer compared to never having a full-term pregnancy. Read more here.