Mixed response, interval from baseline to treatment - 1270961

Thu, 08/27/2015 - 07:43

My husband has stage IV NSCLC with RET fusion, treated with cabozantinib.

Baseline PET/CT scan: 4 weeks before treatment start
Second scan: 7 weeks from treatment start.

Mixed response:
- significantly reduced uptake and size in all previously known tumors
- multiple new spots of uptake: 2 lymph nodes, 5 bone. Bone foci are without a lytic lesion.

Patient is feeling much better.

We can interpret the results as either
(a) some cancer responds, some resistant
(b) progression occurred during the 4 week interval before treatment started, all cancer responds

If we assume (a), then the oncologist recommends adding to the cabozantinib rather than replacing it since it is active and well tolerated.

How likely is (b)?
Is it reasonable to wait for a follow up scan in a month?
What can we lose by waiting?


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Hi snail,

Welcome to GRACE. I'm sorry to hear of your husband's diagnosis. There are two ways to judge the effectiveness of treatment: comparing follow-up scans to those performed prior to treatment, and noting the differences in how a patient appears clinically.

In your husband's case, his improved condition is a very good indication of efficacy of treatment, as is the response shown on the latest scan. In that sense, the possibility you note in (b) is enhanced. It is possible that the cancer had spread to bones even at the time of the first scan, but was not yet visible.

Since your husband is feeling well and the progression, if any, has been relatively slow, there doesn't seem much reason to abandon his current regimen until it becomes clear that significant progression is occurring, and a month is a reasonable amount of time to re-scan.

Good luck with the next scan.

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Thank you, JimC. Seven new metastatic sites, five of them in bones do not sound like slow progression to me...


Judy- I don't know what will be added, that was in an email. Will meet the onc next week. The problem is that there is so little evidence with cabozantinib in RET nsclc, and not many trials used it in combinations. I think that with EGFR and ALK treatments, the recommendation now is to continue beyond progression because once you stop them you might get a "flare up". But those oncogenes are much more addictive and show high response rates to targeted therapy than RET fusion.The combination of cabo with chemo might be less effective than chem alone, and will certainly be more toxic.

My specific question now is what potential harm there is in switching therapy a month later rather then immediately on progression.


When I said that it seemed that progression was not especially rapid, I was taking into account not only the fairly likely possibility that the spread to bones and possibly lymph nodes was not new and the fact that your husband is feeling much better. Of course with the gap between the initial scan and the beginning of treatment, it's hard to know if there is progression or how rapid that progression has been. The risk in waiting a month would be fast progression before you get a chance to change therapies. But the doctors here have often said that in most cases there is no change in outcome if progression is discovered a few weeks earlier, unless it is quite rapid, in which case there will usually be detectable symptoms. In addition, although a swollen lymph node in the context of an existing cancer diagnosis is suspicious for the presence of cancer cells, there can be alternate causes.

Forum moderator


Update: Met the oncologist. He said the response is dramatic and he would continue, in spite of the new mets and increased cough. He suggested we try to escalate dose from 60 mg to 100 mg, although he doesn't expect this to matter a lot.

For those searching for cabozantinib experience (like I did), the main issue we have so far (9 weeks) is hand-foot skin reaction.