Why did only lymph nodes light up on pet scan, If its not lymphoma?

My Mom just had percarditis (fluid around her heart) that just got removed about a month ago. When the percardial fluid was removed they found blood in it, they sent it to a lab and found that it had (VERY FEW) cancer cells. The doctor has said over and over again that she has lung cancer (adenocarcinoma), which just came back negative. She had a PET scan and only lymph nodes lit up and the dr still doesnt believe that it could possibly be lymphoma. I dont understand that if she had any other cancer, why wouldn't have lit up on the PET scan? The dr is now leaning toward pancreas or stomach cancer, which my mother has NO symptoms from either!! Im just very confused. I thought PET scans are very accurate. So please let me know what you think. Thankyou So Much. Chrissy

Your mom has malignant pericarditis. This emedicine article gives the possibilities of various cancers that can cause this condition. Not all cancer types show up on PET scans. Most do, but not all. My best to you and your mom.

http://www.emedicine.com/ped/topic1764.h...

you have lymph nodes all over the body, there are so many different cancer,s out theree they have too take ther time and check every avenue. hope all go well

I had fluid in my chest cavity. After tests and biopsy's they thought I had Hodgkin's disease. It took several weeks for the final tests to come back. I had non-Hodgkin's lymphoma. It was treated with chemotherapy and radiation. That was 21 years ago!
Give them time to get to the root of the problem. Good Luck

Things like infection look like cancer on a PET scan. Also, not every type of cancer will show up on a PET scan. The PET scan works when the patient is given radioactive glucose. Cancer cells divide very rapidly, so they need "fuel". Glucose is that fuel, so they absorb it. The small amount of radioactive material makes these cells light up. Not all cancers reproduce that fast. Some cancers can fester and take their time (lung and pancreatic cancer are both examples) This "slow" moving cancer is actually less treatable than the fast moving ones, because chemotherapy is designed to attack rapidly dividing cells, not ones that fester and spread slowly.

If your mother's lymph nodes lit up, they should probably schedule a biopsy, so they can find out if it's infection (as lymph nodes swell while they fight infection) or cancer. If her oncologist isn't giving you straight answers or you (the both of you) don't feel comfortable with that doctor, you should find someone that you both trust.

Slower growing cancers may not respond as well to a PET scan. In order to grow, a tumor [or cancer] has to 'eat'. At the PET scan, they inject some radioactive dye into you and then you have to rest a while to let the cancerous cells metabolize [eat] the dye. The PET scan shows are the things that 'ate' the dye. In my case, I lit up like a Christmas tree, all lymph nodes in chest area, as well as my tumor [at base of neck], and my spleen. If it is a slower growing cancer of tumor, it may not 'light up' on PET.

Now, I'm not a doctor, that's just what I went through. Here's the best info on Lymphoma, so you can check for other symptoms [esp. itching, night sweats]:
http://www.leukemia-lymphoma.org/hm_lls

Best wishes.