Immunotherapy (Pembro/Keytruda) side effects - decreasing over time or only over a cycle?

Hi - I'm in the same position, with a Stage 2B on my upper arm, with WLE and SLNB on Nov 20.

I have been recommended to start an adjuvant course of pembromizulab (Keytruda) every 3 weeks for 12 months, hard start by 20 Feb (waiting for appointment January 22nd, now the scans are complete.

Will be looking out for responses as I am still unsure whether the risk/reward is right for me.

Hello, I have relevant experience of Pembro. I was diagnosed stage 3B after surgery in April 2024. I started Pembro in July 2024 and had nine treatments over 12 months, so one every six weeks. I’ve had a mixed experience. I didn’t suffer from fatigue at all and the treatments themselves were easy to manage but I did get the following side effects:

- joint pain that began immediately after my second treatment. It was first diagnosed as relating to a long-standing cervical disc issue and not caused by Pembro. I didn’t agree with this - I went to see the osteopath who has treated me previously and she diagnosed carpal tunnel syndrome (which she sorted out quickly and it didn’t return) and shoulder bursitis which I’d never had before. The joint pain is still with me - it’s very debilitating and it’s taken ages to get an appointment with a rheumatologist (next month). If anything, the joint pain has got worse since I finished treatment last July and has spread to my knee and feet. The only relief I get is from short courses of steroids which really help but I keep being told this is not a long term solution - but I have yet to be told what is. Very frustrating and worrying. I feel like the oncology team have been great at sorting out the cancer but not the side effects.

- oral thrush and mucositis. This started after my third treatment. Medication didn’t help until I got prescribed steroids after about six months - it cleared up and I’ve only had a minor issue with it since. 

- Pembro destroyed my thyroid after the first treatment so I am now on levothyroxine for good. It’s inconvenient but liveable with - I take medication first thing and I’ve not really had a problem with it.

- psoriasis. I had a terrible skin reaction on my feet after my final treatment - it was first diagnosed as a fungal infection but it just got worse and had to be treated with very strong steroid creams, which sorted it out eventually and it’s not returned. It was a horrible six weeks though when I found walking quite painful. Subsequently diagnosed as a reaction to the Pembro.

You might assume I regret having immunotherapy. Sometimes I do but mostly I think it was the right course to reduce the chances of further cancer. My scans have all been clear so far. Everyone seems to have a different reaction to the treatment ranging from no side effects to quite serious ones that mean they cannot continue. I’m part of a long term study that is trying to identify who gets what side effects so that future patients can make better informed decisions. 

I’m sorry this isn’t entirely positive but I hope it helps a bit

Thank you so much for taking the time to share this — it’s incredibly helpful to hear honest experience.

I’m really sorry you’ve had to deal with such persistent side effects, especially when support for managing them has lagged behind the cancer care itself. 

I understand that the main benefit with 3 weekly infusions I've been offered is that I’d bemonitored more closely and regularly, so they’d pick things up earlier.

What you’ve said really captures the dilemma: treating an invisible risk to reduce the chance of recurrence, while knowing that immune side effects can be real, sometimes lasting, and unpredictable.

I’m glad you still mostly feel it was the right decision for you.

I appreciate your honesty, and I‘ll think carefully about what support and exit points I’d need in place if I go ahead.

Wishing you luck with the rheumatology review and continued clear scans — and thank you again for sharing!

Hello

My partner had WLE and SLNB both were clear, diagnosed stage 2b. He was offered pembro for 12 months when it was a trial, the other option was watch and wait with regular monitoring at that time for stage 2b.

He decided to go on the pembro trial. He did have side effects if diarrhoea after the first dose, fatigue just after treatment, and sore swollen joints. The pembro kept the melanoma clear for the 12 months, which he was grateful for the trial for, and we saw it as giving him an extra year.

Hope this helps.

Hello I have just had my 6th out of 9 six weekly treatments on Pembro. The minor side  effects ( accept for very tired most mornings, coffee in bed!) hasn’t stopped me doing my usual activities, we have just got back from skiing and I produce cut flowers, lots of gardening and poly tunnel. I go on my e-bike and walk the dogs. I’m retired but very active. Good luck!

This is great to hear - I'm ridiculously active as I'm a stage performer and director (it's only shows in pub theater but it's the world to me) and I really don't want to have to give this up to "beat" a cancer I might not get. 

Thank you Margyy . I'm glad you got that extra year. *hugs*

Hi Webcowgirl

I’ve just had my third dose of Pembro and have so far been very lucky with few side effects. You can read my profile for the full story so far, but basically I’m 75, diagnosed 3b last July, WLE showed a microsatellite close to the lesion on my upper arm, no lymph node involvement, so offered adjuvant treatment, which I started in October - nine sessions, one every six weeks. 

My only side effect up to this week had been mucositis, but I used special over the counter gel and mouthwash and a soft toothbrush, which kept it at bay and it has now diminished so that I am back on the electric toothbrush. This week I developed a small lump under my ear on the jaw line, tender to the touch. Spoke to the nurse on the phone and she thinks it may be a blocked salivary gland, so giving it a week to see if it changes at all. I’ve been feeling a bit weary in the afternoons and have a snooze once or twice a week, but I’ve upped my swimming sessions which may be a partial cause! Bowel movement a bit loose but nothing awful.

I have all my fingers and toes crossed that this positive experience continues. I know the range of experience of immunotherapy among us is huge and no one can anticipate any individual’s reaction. I decided to go for it in the hope that it will prevent reoccurrence - but I know that if it doesn’t reoccur, no one will have any idea if that is down to Pembro or not. So it’s all a bit of a lottery!

Good luck whatever you decide!