Who is this for?
This is for people with melanoma that has spread to lymph nodes or nearby areas but can still be removed by surgery (roughly stage III to early stage IV).
These patients face a high risk of the cancer coming back after surgery, so immunotherapy is given to lower that risk. The usual approach gives it after the operation. This trial asked a deceptively simple question: what if some of it were given before?
What kind of trial is this?
SWOG S1801 was a phase II randomized trial run by a US cooperative research group. Cleverly, it gave both groups the same drug and a similar total amount — the only difference was the timing: some before surgery, or all after. That makes it a clean test of whether when immunotherapy is given matters.
Background: let the immune system see the enemy
Here is the idea. Immunotherapy works by helping immune cells recognize and attack the cancer. If the tumor is still in the body when treatment starts, the immune system can “see” the whole cancer and learn its features — building a stronger, longer-lasting response. Once the tumor is surgically removed, that teaching opportunity is largely gone. So giving some immunotherapy first, before surgery, might work better than giving it all afterward — even with the same drug.
The trial: what was tested and how
SWOG S1801 enrolled 313 people with resectable stage III–IV melanoma, randomly assigned to one of two schedules of the same drug, pembrolizumab:
- Some before, rest after (154 people): 3 doses before surgery, then surgery, then 15 doses after.
- All after (159 people): surgery first, then 18 doses.
The main measure was event-free survival — staying free of the cancer progressing, recurring, or death.
Results: what they found
Giving some immunotherapy before surgery made a striking difference — with no extra side effects.
Same drug — timed differently
Giving a few doses before the operation lowered the chance of the cancer coming back dramatically — a 23-percentage-point improvement.
Both groups received the same drug and a similar total amount. The only difference was when it was given — showing that starting immunotherapy while the tumor is still present matters.
Giving immunotherapy before surgery did not add serious side effects or, importantly, prevent people from having their operation.
Why would timing make such a difference?
When the tumor is still in the body, immunotherapy lets the immune system encounter the full range of the cancer’s features and build a broad, memory-forming response — immune cells that keep patrolling long after surgery to catch any cells left behind. Remove the tumor first, and that training happens with far less material to learn from. Same drug, but a much better teacher when the tumor is present.
Is this the same idea used in other cancers?
Yes — giving immunotherapy around surgery, with some before, has improved outcomes in several cancers, including stomach cancer (MATTERHORN) and triple-negative breast cancer (KEYNOTE-522). S1801 is a particularly clean demonstration because it changed only the timing, not the drug or the amount.
The bottom line
For melanoma removable by surgery, giving some immunotherapy before the operation — instead of all of it afterward — sharply lowered the chance the cancer came back (72% vs 49% cancer-free at 2 years), even though the drug and the total amount were the same. The lesson is about timing: starting immunotherapy while the tumor is still present lets the immune system mount a stronger, more lasting defense. It has helped make neoadjuvant immunotherapy a standard approach for this cancer.
What this could mean for you
- Ask about the sequence. If you have resectable stage III–IV melanoma, it’s worth discussing whether some immunotherapy before surgery is right for you.
- When, not just what. The timing of treatment can matter as much as the treatment itself.
- No added burden. Giving immunotherapy first did not add serious side effects or delay surgery.
Questions & comments
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