Pathologic Complete Response in Lung Cancer: A Milestone, Not a Destination

They’ve had neoadjuvant chemoimmunotherapy. They’ve gotten through the operation. They’re exhausted, relieved, and ready to close the chapter. Then the pathology report comes back with the words everyone wants to hear.

Pathologic complete response (pCR).

No residual viable tumour in the resected specimen.

For many people, it’s hard not to hear that as the finish line.

But the bit we have to be clear about is this:

pCR is a milestone, not a destination.

It’s a strong sign we’ve done well. But it's not a guarantee we’re done.

Why pCR matters, and why it gets misunderstood

In the immunotherapy era, pCR has become a headline metric because it’s tangible. You can point to a specimen and say, “There’s no viable tumour left.”

It is also clearly meaningful for the individual patient. People who achieve pCR generally do better than those who don’t.

The problem is that patients often interpret “complete” as “complete forever”. Clinicians can drift into that too, if we’re not careful, because it feels like a clean endpoint in a messy disease.

But pathology is only telling us what happened in what was removed. It cannot certify the absence of microscopic disease elsewhere.

The 8 to 15% we cannot ignore

This is the bit I come back to with patients who want to stop follow-up after pCR.

A 2026 systematic review by Bardoni et al., looking across neoadjuvant immunotherapy plus or minus chemotherapy studies, reported that recurrence still occurred in 8% to 15% of cases despite pCR, most often as distant relapse.

That one sentence explains why follow-up still matters.

Most people with pCR will not relapse. That’s true. But if you are unlucky enough to be in the 8 to 15%, the timing of detection changes what we can do next.

So when I say, “We still need long-term follow-up,” it’s not pessimism. It’s planning.

Why recurrence can still happen after pCR

If recurrence after pCR feels counterintuitive, it’s because many people assume pathology is a whole-body check. It isn’t.

The most likely explanation is micrometastatic disease. Tiny deposits can exist outside the resection field and never be sampled, never be seen on baseline imaging, and still reappear later.

That fits with what Bardoni et al. highlighted, too. Even when there is no viable tumour in the specimen, pCR does not fully eliminate the risk of later clinical failure, and relapse is commonly distant.

Older long-term datasets in locally advanced disease show the same general principle. In Guberina et al., even among patients with pCR after trimodality therapy, first relapses still occurred, including distant metastases.

So yes, pCR is good news. It’s just not the same thing as zero risk.

pCR is prognostic. But is it a reliable surrogate endpoint?

This is where the research question becomes clinically relevant.

A prognostic marker tells us something about the likely course for a patient.

A surrogate endpoint is a higher bar. It asks whether improving that marker in a trial reliably predicts improvement in outcomes that matter, like event-free survival (EFS) or overall survival (OS).

Huang et al. analysed pathologic response across five randomised trials (2,098 patients) and found that while pCR and MPR can be prognostic in certain groups, they did not demonstrate good surrogacy at the trial level. In other words, treatments that move pCR rates don’t consistently move EFS in a predictable way across studies.

That same theme has been raised in meta-analytic work cited in this space. For example, Waser et al. reported that while EFS correlated moderately to strongly with OS at a trial level, treatment effects on pCR did not show a meaningful correlation with treatment effects on OS or EFS.

So pCR is valuable. It’s just not reliable enough, on its own, to stand in for long-term outcomes.

MPR versus pCR: Similar concept, different threshold

This is worth clarifying, because it changes how we interpret “response”.

• pCR means no residual viable tumour in the resected specimen.
• MPR (major pathologic response) usually means 10% or less residual viable tumour.

So MPR includes pCR, plus a wider group who have responded strongly but not completely.

Why does that matter?

Because in some analyses, MPR may track EFS better than pCR in particular subgroups. Huang et al. reported that in non-squamous NSCLC the correlation between pCR and 2-year EFS was weak (R²=0.55), but the correlation between MPR and 2-year EFS was stronger (R²=0.79).

Bardoni et al. also noted that MPR showed a similar, or in some studies stronger, association with survival than pCR, and suggested MPR can be informative because it captures a broader population of responders.

The clinical translation is straightforward. A near-complete response is still a very good result. But whether it’s pCR or MPR, neither result should be treated as a reason to switch off surveillance.

Why follow-up still matters, even when the news is good

If recurrence after pCR happens in 8 to 15%, the obvious question is: why not focus our energy there?

That’s exactly the point.

Follow-up isn’t about assuming recurrence. It’s about not missing it. Particularly because early detection can keep options open. Depending on the pattern of relapse, that can include systemic therapy, trials, and in selected cases, proactive local treatment.

This is where something like SABR comes in. SABR stands for stereotactic ablative radiotherapy (sometimes also called SBRT). It’s a way of delivering very high-dose, highly precise radiotherapy to a small target over a small number of treatments. In the right patient, and when recurrence is limited in number and location, it can be used to ablate individual sites of disease while minimising dose to surrounding normal tissue. It’s not for everyone and it’s not a magic fix, but for some patients with limited sites of recurrence, detecting relapse early enough can allow a proactive approach rather than waiting until disease is more widespread.

This is where timing really matters. You only get to consider SABR if you detect recurrence early enough that disease is still limited, and the patient is still in good shape to tolerate treatment.

You only get that chance if you’re still looking.

What I tell patients

“We’ve got one of the best pathology results you can get. That’s genuinely excellent news. But it doesn’t take the risk to zero. A small minority of people can still recur, and if that happens, we want to find it early, when we’ve got more options.”

That’s it. No drama. Just the truth.

The takeaway

pCR after neoadjuvant chemoimmunotherapy in resectable NSCLC is worth celebrating. It’s a real milestone.

But based on the available evidence, pCR is not a reliable standalone surrogate endpoint for survival, and it is not a reason to stop long-term follow-up. Because even in the pCR group, 8 to 15% can still recur, often at distant sites, and early detection is what allows us to treat recurrence proactively, including with options like SABR in selected situations.

Milestone, not destination.

About Dr James Wilson

Dr. James Wilson is a Central London–based consultant oncologist specialising in lung cancer and advanced radiotherapy. In his private practice, he provides timely diagnosis, clearly defined treatment strategies, and composed, pragmatic support in critical moments.

References:

1. OncoDaily. (2026, April 3). Is pathologic complete response a reliable surrogate endpoint for survival after neoadjuvant immunotherapy in resectable NSCLC? https://oncodaily.com/oncolibrary/lung-oncology/pathologic-complete-response-elcc2026
2. Woodard, G. A., & Stiles, B. M. (2026). Is major pathologic response the best surrogate end point for neoadjuvant trials? Journal of Clinical Oncology, 44(5), 425–426. https://ascopubs.org/doi/10.1200/JCO-25-01503
3. Huang, N., et al. (2024). Pathologic response as a surrogate end point in oncology trials (Abstract 1235P). Annals of Oncology, 35(Suppl.), S0923-7534(24)02813-8. https://www.annalsofoncology.org/article/S0923-7534(24)02813-8/fulltext
4. Liao, Z., Chen, X., Zhang, Y., et al. (2025). Pathologic response as a surrogate end point for survival following neoadjuvant therapy: A systematic review and meta-analysis. Cancer Communications, 45(1), e70183. https://pmc.ncbi.nlm.nih.gov/articles/PMC12630550/#tca70183-sec-0012