Horses, Not Zebras: Why is Ovarian Cancer Hard to Diagnose?

When doctors are in medical school, one of the phrases they hear about diagnosis is to think “horses, not zebras.” What does this mean? It means when diagnosing someone, look to the most common diagnoses first, not something out of the ordinary. Most of the time, the simplest answer will be what you are looking for, not the rare disease or diagnosis.

Of course, there are times when that ends up not being true. Sometimes, ovarian cancer is the “zebra” that goes undiagnosed. It is known as a silent disease, but that may not always be the case. Symptoms of ovarian cancer often go misinterpreted or ignored as everyday symptoms. This is especially true in the early stages of the disease.

When is ovarian cancer usually diagnosed?

More than 75 percent of women with ovarian cancer are diagnosed at an advanced stage. Most women are diagnosed at stages III or IV. This is because early-stage ovarian cancer often has no apparent symptoms or the symptoms are not specific. There is also no regular screening test for ovarian cancer.^1,2

The difficulty with diagnosing ovarian cancer

One of the main problems with diagnosing ovarian cancer is the lack of clear-cut symptoms. Many times, in early ovarian cancer there either are no symptoms or they are very general. Symptoms often include:²

• Abdominal, back, or pelvic pain
• Bloating
• Constipation and diarrhea
• Stomach upset or indigestion
• Abdominal swelling
• Back pain
• Feeling full
• Frequent urination

Many of these symptoms can be signs of a variety of ailments or even just be everyday aches or pains. They may not cause concern at first. Doctors may consider other diagnoses before thinking of ovarian cancer because the other explanations are more likely.

Primary care doctors may dismiss the symptoms as normal signs of aging or refer you to specialists. Specialists, in turn, may look for things like colon cancer, irritable bowel syndrome (IBS), or endometriosis. This leads to a delay of an accurate diagnosis.

There are no regular screening tests for ovarian cancer like a mammogram. The diagnosis often comes from an imaging test like an ultrasound or CT scan showing a mass. This is usually followed by blood work or a biopsy confirming the cancer. Some women with ovarian cancer do have higher levels of the CA125 protein, but this is not an accurate screening tool. Many different conditions can elevate CA125 levels besides ovarian cancer.^2,3

What you can do

While many doctors may not think of ovarian cancer as a first diagnosis, there are some things you can do to be proactive with your health. Know the symptoms of ovarian cancer, know your risk factors, and let your doctor know about them. If you are not happy with a doctor, seek a second opinion.

Risk factors for ovarian cancer include:^2,3

• Older age
• Genetic mutations
• Family history
• Early menstruation, later menopause, or both
• Not birthing children
• Smoking
• Polycystic ovary syndrome (PCOS)
• Endometriosis
• Obesity

Things to consider

While many doctors may look for horses and not zebras, knowing the risk factors and symptoms of ovarian cancer can help. Knowing this information can help you talk with your doctor about your concerns and seek a second opinion if necessary.