Confusing PET scan after chemo for PMBCL – tumor smaller but SUV increased (possible inflammation?)

Hi everyone, I’m hoping to get some perspective while waiting for my next scan results.

I was treated for Primary Mediastinal B-Cell Lymphoma (PMBCL) and just completed 6 cycles of R-EPOCH.

My interim PET after cycle 4 showed Deauville 3 with SUVmax 3.4, which my doctor considered a good response.

Recently I had another PET scan about 8 days after my last chemo, but it was done at a different imaging center, and the radiologist did not have access to my previous scans for comparison.

The confusing findings were:

• The mediastinal mass shrank slightly (around ~4 cm now)

• But the SUVmax increased to 7.1

One other detail:

On my previous PET, there was also activity near the sternum with SUV around ~5, but that activity appeared to be in the bone of the sternum rather than the tumor itself. We did an MRI afterward which ruled out tumor involvement there, so it was thought to be something benign/inflammatory (my oncologist said it could be PET misreading)

Because the radiologist from this latest PET didn’t have my prior scans, my doctor mentioned that the area of uptake might actually correspond to that same sternum region, which could make the SUV look higher even if the tumor itself is improving.

Other potentially relevant details:

• The final PET scan was done only ~8 days after finishing chemo

• I received one G-CSF injection around Feb 25–26

• The scan was done at a different facility, so protocols may be different and machine is different

Because of all the uncertainty, I’m redoing the PET scan tomorrow at the same center where my previous scans were done so the comparison will be more reliable.

My questions:

1. Has anyone experienced SUV increasing while the mass actually shrinks, and it turned out to be inflammation rather than active lymphoma?
2. How much can timing after chemo or G-CSF affect PET scan uptake?
3. Has anyone had sternum or bone uptake that turned out to be benign?

I’m already scheduled for proton radiation therapy, so we’re trying to clarify this before proceeding.

I know nobody here can give medical advice, but I’d really appreciate hearing if anyone has had a similar experience.

Thanks in advance.