Panic! My PMBCL young adult had a post treatment CT scan to see if his blood clots resolved. The onc team reports...

I can hear the panic in your message, and that's completely understandable. Let me help you understand what's happening here and what questions to ask your team. This situation—growth on CT after treatment—is something oncologists evaluate carefully, and there ARE explanations beyond progression.

Understanding the CT Finding: Growth ≠ Automatic Progression

What you're seeing: Your son finished DA-R-EPOCH (a chemotherapy regimen) in early May, and a recent CT scan shows 1-2 cm of growth in what was being treated. This is genuinely concerning, but here's the critical context:

Why this doesn't automatically mean relapse:

1. Timing matters enormously - Post-treatment scans (especially within weeks of finishing chemo) can show:

   • Inflammatory swelling from treatment effect (the tumor area is healing/dying, which causes temporary inflammation)
   • Residual masses that are actually dead cancer cells, not living cancer
   • Rebound lymphadenopathy (temporary swelling of lymph nodes as the immune system recovers)

2. CT has limitations - CT measures SIZE only. It cannot tell you if cells are alive or dead. A 1-2 cm growth could be:

   • Scar tissue forming
   • Inflammation from treatment
   • Actual disease progression (but this is only ONE possibility)

3. This is exactly why PET scans exist - According to NCCN Guidelines for lymphoma management, PET/CT imaging is used to assess metabolic activity (whether cells are actually alive and growing). A PET scan will show if those 2 cm are metabolically active (concerning) or metabolically inactive (reassuring).

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Your Son's Favorable Signs (Hold onto these)

His MRD tests are GOOD - This is genuinely important:

• MRD (Molecular Residual Disease) testing detects circulating tumor DNA—the actual genetic material from cancer cells in the bloodstream
• Two good MRD tests suggest his bone marrow and blood don't have detectable disease
• According to recent lymphoma research, MRD negativity is one of the strongest predictors of good outcomes

This creates a discordance (mismatch): CT shows growth, but MRD shows no detectable disease. This mismatch actually happens and often favors the MRD result.

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What the PET Scan Will Tell You

The PET scan uses a radioactive tracer (usually FDG) that accumulates in metabolically active cells. According to NCCN Guidelines:

• PET-negative (SUV low) = The growth is likely inflammatory/scar tissue, NOT active cancer. This would be very reassuring.
• PET-positive (SUV elevated) = The growth shows metabolic activity, suggesting viable cancer cells. This would require discussion about next steps.

Timeline context: PET scans done too soon after chemo can also show inflammation, so the timing of when this PET is done matters.

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Questions to Ask Your Oncology Team RIGHT NOW

These are the specific questions that will help you understand what's actually happening:

1. "How long after finishing EPOCH was this CT scan done?" (Timing affects interpretation)

2. "Can you compare this CT to the baseline CT before treatment started?" (Is it growing from baseline, or shrinking but still larger than hoped?)

3. "What are the characteristics of this growth—is it in the same location as the original disease?"

4. "Given that his MRD tests are negative, how do you interpret the discordance between the CT growth and negative MRD?"

5. "When will the PET scan be done, and what will you be looking for specifically?" (SUV values, location, etc.)

6. "What are the possible next steps depending on what the PET shows?" (This helps you prepare mentally for different scenarios)

7. "Is there any chance this is post-treatment inflammation rather than progression?" (Get their honest assessment)

8. "What is the timeline for making treatment decisions—do we wait for PET results before planning anything?"

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What Happens Next (Possible Scenarios)

If PET is negative (most reassuring):

• Likely post-treatment inflammation
• Typically monitored with follow-up imaging in 4-6 weeks
• No immediate treatment change needed

If PET is positive:

• Suggests viable disease
• Your team will discuss salvage options (different chemotherapy, clinical trials, CAR-T therapy, etc.)
• This is NOT the end of the road—PMBCL in young adults has multiple treatment options

If PET is equivocal (unclear):

• May need repeat imaging or other tests
• Your team might recommend close monitoring

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Important Context for PMBCL

Primary Mediastinal B-Cell Lymphoma (PMBCL) in young adults is actually one of the lymphomas with better outcomes when treated aggressively (which DA-R-EPOCH is). The fact that:

• He tolerated EPOCH well enough to finish it
• His MRD is negative
• He's young (better recovery capacity)

...these are all favorable factors.

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Breathing Room: What You Can Do Now

1. Don't make decisions until you have the PET results - The CT alone is incomplete information
2. Bring the MRD results to the PET discussion - Make sure your team is integrating both pieces of data
3. Ask for a tumor board review if you're at a major center - PMBCL cases benefit from multidisciplinary discussion
4. Consider a second opinion from another PMBCL specialist while you wait for PET (this is reasonable and normal)
5. Write down all your questions before the next appointment so you don't forget them in the moment

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The Bottom Line

A 1-2 cm growth on CT after finishing chemotherapy is concerning and warrants investigation—your team is doing the right thing by getting a PET scan. But this is NOT automatically progression. The PET scan will give you much more meaningful information about whether this growth represents active disease or post-treatment changes.

Your son's negative MRD tests are a genuinely good sign that deserves weight in this conversation.

This information is for educational purposes only. Always consult your healthcare team for personalized medical advice and decisions.

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Sources cited:

• NCCN Guidelines for Patients: Marginal Zone Lymphomas (imaging interpretation and PET/CT use)
• OpenOnco: Foresight CLARITY Lymphoma - MRD testing methodology and clinical significance
• PubMed Central: CAR T-cell therapy for B-cell lymphoma (treatment options for relapsed/refractory disease)

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How are YOU doing? This is genuinely scary, and parental anxiety during cancer treatment is real and valid. Do you have support around you?