Ovarian cancer most often begins not in the ovary itself, but in the fallopian tubes, where precancerous changes can quietly develop years before a tumor becomes detectable. The median age at diagnosis is 63, but the biological process that leads to cancer starts much earlier. Understanding this timeline helps explain why this cancer is so difficult to catch early and what factors influence when it develops.
Where It Actually Starts in the Body
For decades, scientists assumed ovarian cancer originated on the surface of the ovary. That understanding has shifted dramatically. The most common and aggressive form, called high-grade serous carcinoma, now appears to begin in the cells lining the far end of the fallopian tube, at the fringed opening closest to the ovary. Abnormal cells at this site form a precancerous lesion known as serous tubal intraepithelial carcinoma, or STIC.
The evidence for this is strong. When researchers examined fallopian tubes removed during preventive surgery in women with BRCA gene mutations, 1 to 7 percent already had these early tubal lesions, and they were consistently located at the fringed end of the tube. Mouse studies have reinforced this: removing the fallopian tubes but leaving the ovaries in place effectively prevented this type of cancer from forming. Not every case starts this way. A smaller number of serous cancers may genuinely originate from the ovarian surface or from tissue related to endometriosis, but the fallopian tube is the primary starting point for most cases.
The Precancerous Phase Can Last Years
One of the most important discoveries about ovarian cancer is that the precancerous stage is not brief. The average time for a STIC lesion to progress into full-blown high-grade serous cancer is roughly 6.5 years. During this window, abnormal cells accumulate genetic damage, particularly mutations in the p53 gene, which normally prevents cells from growing out of control. The earliest change, called a “p53 signature,” involves a stretch of normal-looking tube cells that already carry this mutation. Over time, these cells develop increasingly abnormal features before becoming cancerous.
Once the cancer does become invasive, it grows fast. High-grade serous tumors have a median doubling time of about 2.9 months, with 95 percent of tumors doubling somewhere between every 1.5 and 7.6 months. This means that after years of slow precancerous change, the transition to a rapidly growing, spreading cancer can happen within a relatively short period.
When It’s Typically Diagnosed by Age
Ovarian cancer is predominantly a disease of older women. The median age at diagnosis is 63, and the vast majority of cases occur after menopause. Only about 14 percent of cases are diagnosed in women under 45. Breaking that down further: just 1.5 percent occur in women under 20, about 4.8 percent in women ages 20 to 34, and 7.6 percent in women 35 to 44.
That said, the age when risk begins climbing depends heavily on genetics. Women who carry a BRCA1 mutation are diagnosed at a mean age of 51, with the youngest cases appearing around age 33. For BRCA2 carriers, the mean age at diagnosis is about 61, with the youngest cases around 44. The cumulative lifetime risk is dramatically different too: 49 percent for BRCA1 carriers and 21 percent for BRCA2 carriers, compared to roughly 1.2 percent for women in the general population.
What Influences When It Develops
The total number of times you ovulate over your lifetime is one of the strongest modifiable risk factors. Each ovulation cycle exposes the ovary and fallopian tube to hormonal stimulation and minor tissue damage that requires repair, creating opportunities for genetic errors to accumulate. This is why factors that increase your total number of ovulations raise risk, and factors that reduce them are protective.
Starting periods at age 12 or younger is associated with a 24 to 37 percent higher risk compared to starting after age 16. Reaching menopause at 55 or later raises risk by about 36 percent compared to earlier menopause. A longer overall reproductive span of 40 years or more is independently linked to higher risk. On the protective side, having two or more pregnancies lowers risk, as do years spent on hormonal birth control, both of which suppress ovulation for extended periods.
Why It’s So Hard to Catch Early
The symptoms of ovarian cancer do exist in early stages, but they mimic everyday digestive complaints: bloating, pelvic or abdominal pain, difficulty eating or feeling full quickly, and urinary urgency. The key distinction is persistence. These symptoms occur more than 12 times per month and represent a noticeable change from your normal baseline. Other possible signs include unusual fatigue, back pain, changes in menstrual bleeding, or abdominal swelling accompanied by weight loss.
There is currently no effective screening test for women at average risk. The U.S. Preventive Services Task Force recommends against routine screening using blood tests, ultrasound, or pelvic exams in women without symptoms or known genetic risk. The reason is sobering: the tests generate too many false positives relative to the small number of cancers they find. In a large UK trial, for every one woman correctly identified with ovarian cancer by annual ultrasound, ten additional women underwent unnecessary surgery due to a false alarm. The blood marker CA-125 has similar limitations. It can be elevated by many noncancerous conditions and often fails to catch cancer early enough to improve survival.
This is precisely why the biology matters. The 6.5-year precancerous window theoretically offers time for intervention, but no test currently in clinical use can reliably detect STIC lesions while they’re still confined to the fallopian tube. For women with BRCA mutations, preventive removal of the fallopian tubes and ovaries remains the most effective strategy for reducing risk, and the timing of that surgery is typically guided by when age-specific risk begins to climb for each mutation type.
What the Timeline Means in Practice
Putting all of this together, ovarian cancer follows a pattern: genetic damage begins in the fallopian tube lining, possibly a decade or more before diagnosis. Precancerous changes develop over an average of 6.5 years. Once the cancer becomes invasive, tumor size doubles roughly every three months, and the disease can spread to the abdominal cavity before symptoms become obvious enough to prompt investigation. By the time most women are diagnosed, the cancer has already moved beyond the ovary.
For women with inherited BRCA1 mutations, this process tends to complete earlier, often in their late 40s or 50s. For women without known genetic risk, it typically culminates in the early to mid-60s. The hormonal environment you’ve experienced over your lifetime, particularly the cumulative effect of decades of ovulation, helps determine where on that timeline your personal risk sits.