PET scans and metabolic activity

Factual Questions
1

Hello-

A family member is going through chemo and recently had a PET scan. The tumor has shrunk, and the metabolic activity of the cells has gone from 3.something to 2.6. The doctor says that this is good news. To keep up the patient’s spirits, the doctor seems to present good news without really saying whether it is a little bit good, moderately good, or “OMG! You don’t have cancer anymore!” good. Drawing my own conclusions has led to some disappointment. Asking directly doesn’t get me the information that I want (and I am only second degree next-of-kin, so I can’t really be too pushy when the patient and the next-of-kin are at the appointment as well).

Googling tells me that the metabolic activity rate is higher for cancer cells than regular cells. What I haven’t been able to find is what a rate is for normal cells. I will be much happier if the normal value is 2.5 than if it is 0.001. Is there a baseline? Does it vary based on the type of normal cell it is?

(Nobody here is my doctor; nor are you likely to be my family member’s doctor. If you somehow are, you won’t know which patient I am talking about anyway.)

2

I’m not a radiologist, but the number you’re looking at is a “standard uptake value” or SUV. IIRC, from my husband’s round of PET/CT scans, an SUV over 2.5 is cancerous, and under is not. Naturally, there’s variation from,person to person, but what you describe sounds encouraging.

3

Thanks, gotpasswords. That is a great data point. Having an order of magnitude to look for really helps out. I did read that numbers below six are considered “indolent”, and above 9 are “aggressive”. Indolent is just the kind of cancer I would want, if I had to choose.