Could A New Cancer Scan Help Doctors Better Select Ovarian Cancer Patients For Surgery?

In advanced ovarian cancer, one of the most important questions before planning treatment is: how extensively has the cancer spread?

Ovarian cancer commonly spreads along the thin lining of the abdominal cavity, called the peritoneum. It can form small tumour deposits that may be difficult to detect accurately on conventional imaging.

A newer imaging technique called [68Ga]Ga-FAPI-04 PET/CT, or FAPI PET, may help map this disease more accurately. In our prospective study from Bengaluru, published in the Journal of Nuclear Medicine, we found that FAPI PET performed better than conventional contrast-enhanced CT (CECT) in detecting peritoneal disease in women with ovarian cancer.

Why does this matter in ovarian cancer?

Peritoneal carcinomatosis - the spread of cancer throughout the abdominal lining - is particularly important in ovarian cancer. According to our study, it is present in more than 70% of ovarian cancer cases at diagnosis. The spread can cause symptoms such as abdominal swelling, pain and changes in bowel function, but the extent of disease cannot always be judged accurately from symptoms alone.

Doctors use a measurement called the Peritoneal Cancer Index (PCI) to estimate how much of the abdomen is affected and how large the tumour deposits are. The score divides the abdomen into 13 regions, with a maximum score of 39. Importantly, the location of disease matters, not simply the total amount. Tumour deposits around the bowel, mesentery and certain areas of the upper abdomen can make complete cytoreduction - removal of all visible disease - considerably more difficult.

If imaging underestimates the disease, a patient may undergo a major operation only for surgeons to find that complete cytoreduction is unlikely to be achievable. Better imaging before surgery could therefore help multidisciplinary teams decide between primary cytoreductive surgery and neoadjuvant chemotherapy (NACT), which is chemotherapy given before surgery.

What did our Bengaluru study find?

Our study followed 200 women with epithelial ovarian cancer undergoing evaluation for cytoreductive surgery at a tertiary oncology centre in Bengaluru between May 2024 and April 2025. Nearly nine in 10 had high-grade serous ovarian carcinoma, and 86% underwent imaging after receiving chemotherapy and before interval cytoreductive surgery.

Every patient underwent both FAPI PET/CT and conventional contrast-enhanced CT. The imaging estimates were then compared with what surgeons actually found during surgery, which served as the study's reference standard. The difference was notable.

FAPI PET detected peritoneal disease with a sensitivity of 81.8%, compared with 54.6% for conventional CT. Its overall diagnostic accuracy was 86%, compared with 78% for CT. CT had higher specificity - 96.4% versus 89.3% - meaning it was somewhat better at ruling out disease when disease was absent.

More importantly, FAPI PET was particularly useful in areas where conventional imaging struggles. In the upper abdomen, its sensitivity was 76.5%, compared with just 23.5% for CT. In the small bowel and mesentery, FAPI PET detected disease with 50% sensitivity versus 31.3% for CT. Its correlation with what surgeons found in the small bowel region was also significantly stronger than CT.

Overall, the disease burden estimated on FAPI PET was generally closer to the surgical assessment, while conventional CT tended to underestimate the extent of cancer.

Could this potentially prevent non-therapeutic surgery?

The promise of FAPI PET is not that it makes surgery unnecessary for ovarian cancer. Rather, more accurate preoperative mapping may help doctors identify patients in whom complete cytoreduction is less likely to be achievable and tailor the treatment sequence accordingly.

This distinction is important. Our study did not directly measure how many operations were avoided because of FAPI PET. Instead, the findings suggest that more accurate assessment of disease distribution could improve treatment selection and, if confirmed in further studies, potentially reduce exploratory or non-therapeutic surgical procedures.

When PCI becomes very high, the likelihood of incomplete surgery and major complications rises substantially. Previous evidence cited in our paper found that when PCI exceeded 24, incomplete cytoreduction occurred in 32.7% of patients and major complications in 27%; at PCI above 33, these figures increased to 71.4% and 43%, respectively.

What makes FAPI PET different?

Unlike conventional CT, FAPI PET does not rely only on the size and shape of a tumour. The tracer targets fibroblast activation protein (FAP), which is expressed by cancer-associated fibroblasts surrounding many tumours. This can produce high contrast between tumour-associated tissue and normal background tissue.

There are also practical advantages: FAPI PET has minimal normal bowel uptake, does not require fasting and can be acquired relatively soon after injection.

However, FAPI PET is not yet a replacement for conventional imaging, surgical assessment or multidisciplinary clinical judgment. Our study was conducted at a single centre, used surgical assessment rather than final pathology as its reference standard, and most patients had received chemotherapy before imaging. We also did not directly compare FAPI PET with FDG-PET/CT. Larger prospective studies are needed to establish its role more firmly.

What could this mean for patients?

For patients and their families, the potential value of FAPI PET lies in providing more accurate information before a major operation. Better mapping of the extent and distribution of ovarian cancer may help multidisciplinary teams identify patients who are most likely to benefit from upfront cytoreductive surgery and those who may be better served by chemotherapy before surgery.

Our findings suggest that FAPI PET/CT could become a useful additional tool for preoperative assessment and surgical planning in advanced ovarian cancer. However, it should not currently be viewed as a replacement for conventional imaging, surgical assessment or multidisciplinary clinical judgment. Larger prospective studies are needed to determine whether its improved diagnostic accuracy ultimately translates into fewer non-therapeutic surgeries and better patient outcomes.

(By Dr. Prathap H J, HOD - Nuclear Medicine, PET CT and Advanced Radioligand Theranostics, Aster Hospitals)

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