The menstrual cycle is controlled by the Hypothalamic-Pituitary-Ovarian (HPO) axis, relying on a balance of hormones like estrogen and progesterone. When a period suddenly stops, it is medically termed amenorrhea. While a missed period is often linked to common, non-threatening causes, any significant disruption warrants prompt medical investigation. The reproductive system is highly sensitive to overall health, meaning a severe systemic illness can manifest as a cessation of menstrual flow. This article explores how cancer and its treatments can disrupt this cycle, alongside a review of more common causes.
How Cancer Disrupts the Menstrual Cycle
Cancer can directly interfere with the hormonal signals that regulate the menstrual cycle, sometimes even before treatment begins. This disruption occurs when a tumor affects hormone-controlling glands, such as the hypothalamus, pituitary gland, or the ovaries. For example, a noncancerous tumor in the pituitary gland, like a prolactinoma, can overproduce prolactin. This suppresses the release of gonadotropin-releasing hormone (GnRH) from the hypothalamus, halting ovulation and menstruation.
Cancers arising in the ovaries can cause irregularities by directly altering local hormone levels. Adrenal gland cancers can secrete excessive hormones like cortisol or androgens, which disrupt the HPO axis feedback loops and stop the cycle. Advanced or systemic cancer also causes severe physiological stress, malnutrition, or profound weight loss. This systemic stress can trigger functional hypothalamic amenorrhea, where the brain shuts down reproductive function as a survival mechanism.
Impact of Cancer Therapies on Ovarian Function
For patients with a cancer diagnosis, the most frequent cause of amenorrhea is the treatment used to combat the disease. Cytotoxic chemotherapy agents kill rapidly dividing cells, including the sensitive ovarian follicles. Damage to these follicles leads to premature ovarian insufficiency (POI), resulting in chemotherapy-induced amenorrhea (CIA).
The risk of CIA depends on the patient’s age and the specific drugs and dosages used; older patients and those receiving high-risk agents face a greater chance of permanent amenorrhea. Radiation therapy directed at the pelvic area can destroy ovarian tissue. Radiation aimed at the brain can also damage the pituitary or hypothalamus, disrupting the central control of the HPO axis.
Hormone-sensitive cancers, such as breast cancer, are treated with therapies that intentionally suppress ovarian function. Medications like tamoxifen or LHRH agonists suppress estrogen production, which can cause irregular periods or complete cessation of menses.
Other Common Reasons for Amenorrhea
Cancer is a rare cause of a missed period, as many other factors frequently cause amenorrhea. Pregnancy is the most common reason for secondary amenorrhea, defined as the absence of a period for three or more consecutive months. Fluctuations in body weight, whether loss or gain, can interrupt the cycle by altering energy balance and hormone levels.
Conditions involving other endocrine glands frequently cause menstrual changes. An overactive or underactive thyroid gland can interfere with hormone regulation and lead to irregularities. Polycystic Ovary Syndrome (PCOS) causes hormonal imbalance, often resulting in irregular or absent periods. High psychological or physical stress can also induce hypothalamic amenorrhea by suppressing the GnRH signal.
When to Consult a Healthcare Provider
Any sustained change in the menstrual cycle should be discussed with a healthcare provider to determine the underlying cause. If a period is missed for three or more consecutive cycles without a clear physiological reason, a medical evaluation is warranted.
It is important to seek prompt consultation if amenorrhea is accompanied by other unexplained symptoms. These potential red flags include:
- Persistent, unexplained pelvic pain.
- A feeling of being full quickly, or chronic bloating that does not resolve.
- Unexplained weight loss or severe fatigue.
- The development of new, unusual pain.
For individuals who have gone through menopause, any instance of bleeding or spotting must be investigated immediately. Postmenopausal bleeding is never considered normal and can be a sign of uterine or cervical cancer.