Q. Kindly explain non-FDG avid in a PET scan of a breast cancer patient.

Answered by
Dr. Arshad Hussain Shah
and medically reviewed by iCliniq medical review team.
This is a premium question & answer published on Sep 12, 2020

Hi doctor,

My mother had breast cancer 13 years back, and this year again she has been diagnosed with bone only metastasis as per the report. She is currently on Letrozole and Ibrance for the last five months. Initially there was bone pain near pelvic, and so did the ultrasound, in that it came minimal ascites, following that we did CA 125 @ 104 and CEA @ 47 five months back, followed by CT and PET CT scan and biopsy (the biopsy was done from bone and not from omental which came positive for breast cancer origin and negative for colon and intestine CA. In both, there were two observations. Non-FDG avid bone and generalized haziness.

What is non-FDG avid that is described in PET scan? What is a generalized haziness, omental metastasis from breast cancer? What can be the cause? Before two months, we repeated CA 125 which came 33 from 104 at initial diagnosis 2 CEA @ 29, 47 at the initial diagnoses.



Welcome to

I can understand your concern regarding the new findings on CT PET Scan of your mother. She is having multiple bony metastases proven radiologically and pathologically. The generalized mesenteric and omental haziness with raised tumor markers Ca 125 / CEA, these findings raises suspicion of peritoneal involvement. But, there is no clear nodule or mass found in the abdominal cavity. So she needs a close follow-up and further investigations.

She has proven bone metastasis as confirmed pathologically and radiologically (CT scan) with out uptake of FDG. Non FDG avid means her some bone metastasis have not taken up FDG. Usually, tumor and the metastatic site takes up FDG But here bone metastasis has been confirmed already by CT scan and biopsy. At this stage, I would suggest you discuss with your oncologist for a possible laparoscopic evaluation of the abdomen (peritonuem, omentum, and mesentery). It will show any visible suspected lesion in the abdomen and biopsies can be taken from any suspicious lesions or she can be put on close follow up and a PET CT and tumor markers can be repeated after two months. They should also drain the abdominal fluid and send it for analysis (cytology for malignant cells).

Also, she may need transvaginal ultrasound that is very sensitive to detect any ovarian tumor. Because ovary is one of the common causes of peritoneal and omental involvement. She may also need to do an MRI whole spine as there are multiple vertebrae (spine) metastasis. There is a risk of spinal cord compression and MRI can detect it early. Did she have a previous surgery of the uterus or ovaries or any abdominal surgery?

Thank you doctor,

The uterus was removed many years ago. If it is non-avid, is it an indolent or low grade or slow CA? According to current reports, do you think omental involvement is 100 % there or it is suspicious? The oncologist has told us to do an ultrasound to check the progress and he does not think ovaries or other organ is involved, he told this CA had omental involved, and moreover, the treatment will be same. What is the prognosis of such CA? We repeated the test of ca 125 before two months which came 33 and at the time of the diagnosis it was 104 before five months, does it indicate anything?



Welcome back to

Yes, non-FDG avid usually means low-gradetumor. But, here it does not apply because bones are her metastatic sites and metastatic tumors follow same grade and pathology as the primarytumor. Regarding omental involvement, it is highly suspicious and not confirmed yet. In case omentum is involved, then the malignancy is advanced and the prognosis is poor. Peritoneum and omental are usually involved if a primarytumor is a lobular carcinoma rather than ductal. Tumor markers are not very much high. In case they are doubling in the shortperiod, then there is definitely pathology in the peritoneum or ovarian regions.

Thank you doctor,

In case the omentum is involved, can it be resolved with the current medication? Is it possible in the near future for better treatments for such a condition? In the last 4 to 5 months, since it was diagnosed, the patient weight increased from 75 to 79, active, tumor marker down. I am wondering if the omental was involved by this time it would have been detected or had symptoms? I am wondering if our oncologist believed it was very serious, then why has he kept on the first line therapy, Letrozole and Ibrance, and monthly injection. According to the report 13 years back, the carcinoma was mixed lobular and ductal. Basically, how much time does it take tumor to grow if not detected clearly in PET/CT scan? I have read that early omental disease shows as diffuse haziness on the CT scan. Is it true?



Welcome back to

In case the omentum is involved, the disease is incurable and the chances of complete resolution of disease are slim. But with cancer medicine, it can be controlled and the progression can be delayed. Patient with omental disease from breast cancer, the average survival is 18 months. But in her case, the omental and peritoneal involvement is highly suspicious but not confirmed. Only 15 % of patients with omental or peritoneal involvement can survive for five years. Many clinical trials are going on and in the coming years, better and revolutionary treatment is expected. The weight gain, good appetite, decreased tumor markers and pain control without medicine or with occasional analgesic, are good clinical signs and it indicates a good clinical response to the treatment. So that is the reason in her case, that her oncologist is continuing with the same medicine.

In case there was a micro peritoneal or omental disease and the medicine she took was not working, in that case, the disease could have become visible and palpable with worsening symptoms in a few months time. Letrozole and Ibrance are the best treatment for post-menopausal women with metastatic breast ca ER-positive and HER 2 negative. In case there is a micro or small omental and peritoneal disease and the patient is not responding to the treatment, it will become visible on radiological imaging in three months time. The golden standard to diagnose a peritoneal or omental disease is through laparoscopy. By other techniques like PET CT, ultrasound, MRI, etc., it can be missed if there is micro disease or small metastasis.

Thank you doctor,

We had an ultrasound and it came back normal, though it says minimal free fluid in the pelvis in the intrabowel space. At the time of diagnosistoo, it said minimal ascites. This time radiologist checked for omental as it was written on the doctor's prescription, she said there is nothing abnormal. What is the minimal free fluid in the pelvis in intrabowel space?



Welcome back to

The ultrasound report is showing no peritoneal or omental pathology (no masses or nodules). Minimal free fluid in the pelvis in the intrabowel space is a non-specific finding. Anything that causes inflammation of the organs in the pelvis can be associated with minimal to moderate free fluid in the pelvis. Most of them are benign conditions. So, I would suggest to repeat ultrasound after 45 days and compare it with the previous one. It looks that there is no gross pathology in the abdomen (omentum or peritoneal cavity).

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