From Cancer to Stroke — What Mami Yamase’s Ordeal Reveals About Women’s Health in Modern Japan

Endometrial Cancer, Breast Cancer — The Increased Health Risks Faced by Women Who Have Never Given Birth

Talent Mami Yamase (56) has revealed that she suffered a cerebral infarction during surgery for endometrial cancer, a confession that has sent shockwaves through the public.

Although Yamase was married, she has never given birth — and endometrial cancer is known to occur more frequently in women who have not experienced pregnancy. In Japan and other developed countries, trends toward later marriage, remaining single, and choosing not to have children are increasing. Dr. Yuki Sekiguchi, director of the Women’s Medical Clinic LUNA, points out the health risks linked to these lifestyle changes.

⬛︎Endomerial Cancer

In Japan, approximately 18,000 women are diagnosed with endometrial cancer each year, and the number continues to rise. Behind this trend are changes in women’s lifestyles and hormonal environments.

“Endometrial cancer develops from the uterine lining and is most commonly seen in women in their 40s to 60s, around the time of menopause. Postmenopausal bleeding is an extremely important warning sign. Even light or intermittent bleeding should prompt an immediate visit to a gynecologist. For premenopausal women, any bleeding outside of regular menstruation should also be taken seriously.

If detected early, endometrial cancer has a five-year survival rate of over 90%. The most important thing is not to self-diagnose — seek medical attention right away.”

Why Not Having Children Raises the Risk? The key lies in the female hormone estrogen.

“Women who do not experience pregnancy, childbirth, or breastfeeding are exposed to estrogen for a much longer period. While estrogen is essential for maintaining the female body, excessive exposure can increase the risk of abnormal cell growth.

During pregnancy, childbirth, and breastfeeding, ovulation and menstruation stop for a time, reducing total estrogen exposure. Conversely, women who have never given birth have longer cumulative menstrual years, meaning that the cells of the uterus and breasts are exposed to hormones for longer. As a result, they face a higher risk of endometrial cancer, uterine fibroids, and breast cancer.”

Visit the gynecologist before you start feeling unwell

⬛︎Uterine Fibroids

Uterine fibroids, benign tumors that form when part of the uterine muscle develops into nodules, are strongly influenced by estrogen and are more common in women who have never given birth.

“Fibroids grow slowly and often cause few symptoms, so they’re frequently discovered by chance during checkups or ultrasound exams. Although they’re not life-threatening, if left untreated, they can grow to the size of a baby’s head. If you notice heavier menstrual bleeding or changes in period pain, I recommend visiting a gynecologist early.”

⬛︎Endometriosis

Endometriosis is another condition linked to the absence of pregnancy, with an estimated 2.6 million patients in Japan — a number that continues to rise.

“Endometriosis occurs when tissue similar to the uterine lining grows and sheds repeatedly outside the uterus, such as on the ovaries or peritoneum. It tends to occur more frequently in women who have never been pregnant. When it develops on the ovaries, it can form cysts called chocolate cysts, which become increasingly painful over time.

Many women endure their period pain, thinking it’s just part of the month. But if your cramps are getting worse year after year, endometriosis could be the cause. Left untreated, it can lead to reduced ovarian function or infertility, so early diagnosis and treatment are vital.”

⬛︎ Breast Cancer

Breast cancer is the most common cancer among Japanese women. The risk is higher for those who have never given birth, started menstruating early, experienced late menopause, or are overweight — all of which are linked to prolonged estrogen exposure.

“These are general statistical trends — whether a woman has given birth or not does not solely determine her risk. Lifestyle habits, body type, and genetics also play major roles. When detected early, more than 90% of breast cancers are curable. Perform a self-exam once a month and have regular mammograms starting at age 40. If there’s a family history of breast cancer, consider screening from your 30s.”

While the absence of childbirth can be one factor, a combination of genetics, body constitution, lifestyle, and weightshapes each woman’s unique risk profile. What matters most is understanding your own risks and connecting that awareness to early detection and treatment.

“Whether or not you choose to have children, I want women to think of gynecology not as a place to go when something’s wrong, but as a lifelong partner in health. Even small changes are worth discussing early — it can make a world of difference in treatment options.”

In today’s Japan — where late marriage, remaining single, and declining birthrates continue to rise — choosing not to have children is a personal decision that deserves full respect. Yet it’s equally important to understand how that choice affects hormonal balance, maintain regular checkups, and make informed health and life plans.

Yuki Sekiguchi
After graduating from Yamagata University School of Medicine, Dr. Yuki Sekiguchi completed her doctoral program at Yokohama City University Graduate School of Medicine. She is the Director of Women’s Medical Clinic LUNA and a Visiting Professor at Yokohama City University Graduate School. A specialist in female urology and postmenopausal medicine, Dr. Sekiguchi provides comprehensive care tailored to women at every stage of life. As the Representative Director of the Japan Femtech Association, she actively promotes the advancement of femtech, while also being a certified testosterone therapy physician with the Japan Men’s Health Medicine Society, demonstrating expertise in male menopause treatment as well.