A woman’s supposed pregnancy turned out to be something much stranger. In a recent report from her doctors, they detail how the woman had developed an incredibly rare form of ovarian cancer that mimicked the symptoms of pregnancy, even causing a positive pregnancy test.

Doctors in India described the case of mistaken identity earlier this July in the journal Oncoscience. After first suspecting the woman had an ectopic pregnancy, the doctors instead discovered a large and rare type of tumor in her right ovary. Thankfully, the cancer was removed before it spread elsewhere, and the woman seems to have responded well to treatment.

A pregnancy that wasn’t

According to the report, the 36-year-old woman visited doctors three months into having intermittent bouts of heavy menstrual bleeding. She tested positive for a pregnancy on a urine test, and when doctors performed a physical examination, they felt a solid mass along her abdomen consistent with having a 20-week-old fetus. An initial ultrasound appeared to show that the woman was experiencing an ectopic pregnancy, a condition where the embryo forms outside of the uterus, usually in the fallopian tube (ectopic pregnancies are inherently non-viable). After conducting more extensive imaging, they found that she actually had cancer in her right ovary, most likely a choriocarcinoma.

Choriocarcinomas are tumors mainly formed from the cells that become the placenta during a pregnancy. It’s an especially dangerous cancer since the tumors tend to grow quickly and spread to other parts of the body. The woman’s doctors soon performed surgery to assess the progression of her cancer and to treat it if possible.

They successfully removed the tumor, along with the woman’s uterus, ovaries, and surrounding lymph nodes. Though relatively large, the tumor was still in an early stage of development and hadn’t metastasized. When the doctors looked closer, though, they found her cancer was even weirder than first thought.

‘Exceedingly rare’

Choriocarcinomas are usually gestational, meaning they’re linked to pregnancy; oftentimes, the tumor will even arise from an abnormal and non-viable pregnancy. But the woman’s cancer was a non-gestational ovarian choriocarcinoma (NGOC), which only accounts for 0.6% of all reported ovarian germ cell tumors (a germ cell being the actual egg). What’s more, the cancer was a pure NGOC, an “exceedingly rare” subtype made completely out of germ cells and not any other kinds of tissues.

An image of the woman’s tumor, as well as her uterus and a benign ovarian cyst, can be seen here, but be warned, it’s not for the faint of heart.

While these cancers aren’t tied to pregnancy, they do cause the body to produce high levels of the hormone human chorionic gonadotropin (hCG). Women also produce high levels of hCG during pregnancy, and some tests detect pregnancy through measuring hCG, explaining the woman’s positive result.

“NGOC is a rare, distinct, and highly aggressive tumor that predominantly affects young, reproductive-aged women,” the authors wrote.

Fortunately, in this case, the cancer appears to have been caught early enough in time. Following surgery, the woman was placed on chemotherapy. And her most recent tests showed that her hCG level had returned to normal, indicating a complete treatment response, according to the doctors. She will need to have regular follow-up tests, including CT imaging, to make sure the cancer isn’t staging an unwelcome comeback.