She says early formulations of the therapy increased a woman's risk of endometrial cancer.
Less commonly endometrial growths may also be found in the lung, arm or thigh.
"Let's not diminish the effect of tamoxifen by this side effect, " said Peters, referring to endometrial cancer.
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Endometrial tissue builds up during the menstrual cycle, and then breaks down and sheds off during a period.
In the past, studies have shown that taking oestrogen can also increase a woman's risk of endometrial cancer.
Endometrial polyps are removed to treat the abnormal bleeding but also because of the potential risk of cancer.
In a pilot study, they analyzed Pap smears from 46 women who already were diagnosed with either ovarian or endometrial cancer.
Endometrial cancer affects about 47, 000 women a year, and kills about 8, 000.
Mortality seemed to be higher for many types of cancer, but it was only statistically significant for three types: breast, endometrial, and colorectal.
The new technique found all the endometrial cancers and 41 percent of the ovarian tumors, the team reported Wednesday in the journal Science Translational Medicine.
Oestrogen has already been linked to breast, endometrial and ovarian cancer.
The endometrial cancers may have been easier to find because cells from those tumors don't have as far to travel as ovarian cancer cells, Diaz said.
For example, higher levels of the female sex hormone estrogen can stimulate the growth of breast and endometrial cancers, and fat cells are known to produce estrogen.
By suppressing ovulation, it actually reduces the risk of two types of cancer: ovarian, which affects the ovaries and endometrial, which affects the lining of the uterus.
Clare Stevinson, a Cancer Research UK researcher at the department of exercise and health sciences at the University of Bristol, said the findings of the endometrial cancer research were "encouraging".
Irregular bleeding can also be the result of endometrial polyps, overgrowths in the lining of the uterus, and can even be a sign of pre-cancer or cancer of the uterus.
Endometrial polyps are typically identified during the evaluation of abnormal bleeding and may be found either on ultrasound or by endometrial biopsy, an office procedure that samples the lining of the uterus.
There is also evidence that oral contraceptives decrease the risk of ovarian and endometrial cancer, but that they increase the risk of liver cancer in women who are otherwise considered at low risk for the disease.
Obesity and the state of being overweight substantially raises their risk of morbidity from hypertension, dyslipidemia, type 2 diabetes, coronary heart disease, stroke, gallbladder disease, osteoarthritis, sleep apnea and respiratory problems, and endometrial, breast, prostate, and colon cancers.
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Dr Amy Berrington, of Cancer Research UK, said the link between oral contraceptive use and cancer risk was highly complex, with studies showing that taking the Pill reduced ovarian and endometrial cancer risk, but increased the risk of breast cancer risk and probably also cervical cancer.
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