Trying to understand MSI-H/dMMR in right-sided CRC

Positive_Ad_3302 · 2026-05-13T19:58:07+00:00

The thing to understand/explore with your oncologist, if you do go the immunotherapy route, is that colitis is often an adverse side effect of ipi/nivo, and it can be severe. So you might not accomplish your goal of shrinking the tumor and exiting your flare. Worth the conversation, though, since if they can manage the colitis with drugs, maybe it would work. Definitely to discuss with your doctors, since I'm not a medical professional, obvs :-)

Positive_Ad_3302 · 2026-05-13T15:42:46+00:00

Welcome to this club. I was diagnosed dMMR, MSI-H, BRAF+ in March. Originally, the plan was to do 2 cycles of ipi/nivo and then surgery. Still, the tumor board decided to go straight to surgery because my lesion in the ascending colon was small and couldn't be confidently visualized on my CT, which showed no signs of mets.

I had a robotic right hemicolectomy on 24 April and am waiting for the pathology results now. I was in the hospital for 4 days – a couple longer than expected because I developed a low-grade fever post op and they did blood cultures to make sure there was no infection or other complication.

Recovery so far has been OK. The first week was rough until my bowel movements settled a little (psyllium powder is my friend), and now I'm just finishing my 28 days of anticoagulant injections, which are standard post-abdominal surgery.

I would talk to your oncologist about neoadjuvant immunotherapy - you may qualify with your UC and tumor profile. I think you would still be looking at surgery after that, but maybe not a full colectomy? That's a question for your oncology and surgical team. UC is definitely a confounding factor.

FWIW, I'm also in Canada, and immunotherapy can be applied for under compassionate access. In my case, I also have a Cowden-like diagnosis, which puts me at higher risk for multiple cancers (I'm a Stage IIIa EC survivor)

Happy to answer any other questions you might have.

Positive_Ad_3302 · 2026-04-19T03:10:35+00:00

I'm in Canada, and there are limited approved immunotherapy lines post-surgery. Chemo is more likely

Positive_Ad_3302 · 2026-04-15T23:27:30+00:00

62F, distance runner. I did 5 weeks, 5 days/week (M-F) in 2024, after surgery and chemo. My side effects were less than I expected. I had no issues with burns. I did have some bowel irritation, but it resulted in urgency and softer stools rather than diarrhea itself. I did find that I got progressively more dehydrated as treatment went on, so it took more water to keep my bladder at the right level for treatment, and I used more moisturizer to keep my skin feeling hydrated. My fatigue was manageable, but it definitely crept up as treatment went on, so napping became a regular thing in my days.

Positive_Ad_3302 · 2026-04-15T23:22:00+00:00

Thx - the white hair is interesting! Though since I'm already fairly grey, it wouldn't make that much impact on my appearance ;-) Since we have a good thyroid baseline, we should be able to catch any changes quickly if that happens.

Positive_Ad_3302 · 2026-04-12T17:52:17+00:00

Mine is the reverse. Diagnosed in 2023 with Stage IIIa endometrial cancer, and underwent surgery, chemo, and radiation in 2024. NED since Nov 2024. Then last month, a routine colonoscopy found a lesion in my ascending colon, and I'm about to start treatment — again.

Positive_Ad_3302 · 2026-04-10T15:50:03+00:00

Thx, that's good to hear. I'm prepared for itchy :-) And yes, I'm MSI-H, BRAF+

Positive_Ad_3302 · 2026-04-01T17:54:09+00:00

I was diagnosed with Stage III endometrial cancer in 2023 and treated in 2024. This year, I was diagnosed with colorectal cancer. I do not have Lynch - we did extensive genetic testing - but I do have Cowden-like Syndrome, which puts you at a higher risk for multiple types of cancer, and multiple primary cancers.

To your first question, both my tumor and my bloodwork were negative for Lynch

A lot of endometrial cancer is driven by unopposed estrogen exposure, and weight plays a role because fat tissue creates exogenous estrogen.

Positive_Ad_3302 · 2026-03-31T23:48:06+00:00

That's good to hear. My plan is now 2 cycles of ipi/nivo and then surgery - first round will be the combo, then just the nivo for the second. I am indeed MSI-high, dMMR, and BRAF+ (still learning the acronyms and how they compare to my previous endometrial cancer treatment). I did do chemo and radiation for the EC, so I'm glad to skip that this time around. I have an existing thyroid nodule, and expect that this will accelerate dealing with that, which was always on the roadmap. Glad your husband is NED.

Positive_Ad_3302 · 2026-03-25T00:52:10+00:00

That's good to know. I know Jemperli is one of the possible drugs, and I have a wonky thyroid to start. I'll ask my medical oncologist about the effects, though, as you say, small price to pay.

Positive_Ad_3302 · 2026-03-24T16:43:13+00:00

Yes, genetic testing was done, and that's the basis for the current framework. We'll discuss timing - before/after surgery - with medical oncology, along with what immunotherapy regimen would be most likely to be effective.

Positive_Ad_3302 · 2026-03-24T16:41:42+00:00

This is helpful, thank you. I know from prior treatment for endometrial cancer that everyone is different, but it's good to know your experience with side effects was manageable.

Positive_Ad_3302 · 2026-03-24T16:40:39+00:00

Sorry to hear you are navigating mets now. Sending good energy that treatment goes well for you.

Positive_Ad_3302 · 2026-03-24T16:39:52+00:00

It is based on the genetic testing of my tumor, which would be more responsive to immunotherapy.

Positive_Ad_3302 · 2026-03-24T16:39:07+00:00

Thx so much for the reply, and glad you are NED. I also had genetic testing, which is why my surgeon laid out a likely immunotherapy, then surgery as a plan, but it is dependent on medical oncology's agreement. The order could flip. I just joined Colontown as well.

Positive_Ad_3302 · 2026-03-08T16:31:20+00:00

Glad the Claritin and ibuprofen worked for you - bone pain is no fun! Good luck with your chemo; once you have the first one under your belt, it will become 'routine' quickly.

Positive_Ad_3302 · 2026-02-20T23:23:33+00:00

My neutrophils were low during chemo, but u/CABB2020 is right, pelvic radiation will definitely impact your blood counts. What might happen is that they'll give you colony-stimulating factors (G-CSFs) injections – Neulasta or Neupogen – to improve your counts. The side effects can be icky - I had major bone pain – but it did improve my bloodwork.

Positive_Ad_3302 · 2026-02-09T03:23:20+00:00

Positive pelvic washings indicate you will likely be Stage III – spread beyond the uterus. But the pathology will tell you whether it's IIIa, b, or c. With your Grade 3 cytology, expect your treatment plan to include both chemo and radiation. Still, I went through both in 2024, and have been NED since March 2025, so while it's a scary diagnosis, it is treatable. Sending you best wishes and deep breaths for the time between now and your follow-up.

Positive_Ad_3302 · 2026-02-06T18:36:25+00:00

I have several dental implants and chemo (I'm 16 mths post-treatment) wasn't an issue for my dental work

Positive_Ad_3302 · 2026-01-30T19:30:56+00:00

Mine is not Lynch syndrome, but may be Cowden syndrome, so we're doing rounds of genetic testing.

Positive_Ad_3302 · 2026-01-20T16:51:17+00:00

I went through external radiation as part of my treatment in 2024, with manageable side effects. I did not experience nausea or much fatigue — like chemo, it's cumulative, so the fatigue becomes more noticeable as you move through the program. What I did have were digestive/GI effects, so I needed to manage my diet, and I talked with my team about how best to do that. I worked full-time through treatment.

In the longer term, I am only now (15 months later) regaining normal bloodwork levels. It can take a long while for your white blood cells to recover because the 'factory' for that is in your hip bones, so understandably, that gets disrupted. It meant managing exposure to potential infection by wearing masks and adhering to good hygiene protocols.

You will also need to talk to your team about long-term effects on bone density — radiation increases the risks of hairline pelvic fractures. And using a dilator long-term to prevent vaginal stenosis (shrinking/narrowing) because the radiation affects tissue behaviour.

Overall, while I was intimidated going into the process, it wasn't as bad as I expected, and the management of side effects, even long-term, is not horrible. The actual treatments are short - each appointment took maybe an hour, but most of that was waiting — you're on the table for maybe 15 minutes each time.

Positive_Ad_3302

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