Minimal residual disease: why every gram of tumor matters

In short: In the previous article I wrote about the grey zone – anecdotal observations, honestly labeled as such. This article is the opposite: an idea backed by randomized trials, one I believe patients hear far too little about. The idea: the total amount of tumor in your body is not just a staging number. It’s a strategic variable – and there are serious arguments that reducing it as much as possible, as early as possible, with every tool available, changes your odds. Including the uncomfortable part: the trials that say otherwise.

A simple question nobody asks out loud

When you’re diagnosed with metastatic cancer, systemic treatment – targeted pill, chemotherapy, immunotherapy – becomes the center of the world. Radiotherapy and other local treatments usually enter the conversation only “when needed”: when a lesion hurts, when it grows, when it threatens something.

The question I eventually came to ask myself: why “when needed”? If systemic treatment keeps the disease under control but doesn’t wipe it out completely, what happens to what’s left? A reservoir remains. And that reservoir is not passive.

Why volume matters: three mechanisms

1. The resistance lottery. Treatment resistance arises through random mutations. And in that lottery, every extra tumor cell is an extra ticket – it’s an idea four decades old in oncology (the Goldie-Coldman hypothesis): the probability that a resistant cell already exists somewhere in the body grows with the total number of cells. Less tumor = fewer tickets = more time before the treatment gives out.

Even more interesting: each lesion is a separate evolutionary reservoir , developing its own mutations, independently of the others. In one melanoma patient, three different lesions developed three different resistance mechanisms , simultaneously. Every lesion you eliminate isn’t just “less disease” – it’s a resistance laboratory shut down.

2. High volume smothers immunity. The immune system fights cancer every day, but the fight wears it down. Studies show that a high tumor burden exhausts T cells – pushing them into an “exhaustion” state they recover from with difficulty – and that patients with high tumor volume respond worse to immunotherapy . Less tumor doesn’t just mean less enemy; it means an immune system that’s less overwhelmed.

3. Residual lesions harbor the survivors. Even when targeted treatment works spectacularly, the remaining lesions hide drug-tolerant cells – not mutants, just adapted, in partial hibernation. From them, true genetic resistance is later born . That “stable, small, we won’t touch it” lesion on your report is exactly their shelter.

The lesson hematology learned decades ago

In leukemias, this idea has a name and sits at the center of treatment: minimal residual disease (MRD). In chronic myeloid leukemia, the explicit target isn’t “the patient feels fine” – it’s reducing the disease by four orders of magnitude, measured molecularly , because the depth of response predicts survival and even the chance of stopping treatment. In acute leukemia, therapy is escalated or de-escalated based on MRD .

In solid tumors, the equivalent is only now being built: circulating tumor DNA (ctDNA) in the blood. The data are already impressive as prognosis – patients whose ctDNA clears on treatment have a threefold lower risk of progression , and ctDNA can announce relapse months before the scan . The honest label: for now ctDNA predicts, but no trial has yet shown that acting on it prolongs life. It’s the direction, not the standard.

But the principle behind it – the depth of the response matters, not just its direction – strikes me as the most important idea a solid-tumor patient can borrow from hematology.

The evidence: what happens when you ablate the residual

Here we’re no longer in the grey zone. Randomized trials:

• SABR-COMET (various cancers, 1-5 metastases): stereotactic radiotherapy to all lesions doubled long-term survival – at 8 years, 27% of aggressively treated patients were alive, versus 14% in the standard group.
• Gomez (lung cancer, up to 3 lesions remaining after initial treatment): local consolidation moved median survival from 17 to 41 months .
• SINDAS (phase 3, EGFR-mutant lung cancer on a targeted pill): stereotactic radiotherapy done upfront, to all lesions, not on demand, extended survival from 17.4 to 25.5 months – with acceptable toxicity. It’s the trial closest to the situation of patients with “driver-dependent” disease, like mine.
• And when the disease escapes in just a few spots under targeted treatment, the strategy of ablating them and continuing the same pill – dubbed by oncologists “weeding the garden” – is today recommended by guidelines : you pull out the resistant weeds and keep the treatment that controls the rest of the garden.

Where caution gets it right – the part other articles leave out

If I stopped here, this article would be propaganda. The full picture:

• NRG-LU002, the most recent large American trial, tested exactly this aggressive consolidation in lung cancer patients – most on immunotherapy – and came out completely negative : zero benefit.
• CURB showed that in oligoprogressive lung cancer radiotherapy quadrupled time to progression, but in breast cancer it delivered nothing . The biology of the disease decides – “radiate everything” is not a universal rule.
• SABR-COMET itself has serious critiques : a small trial, imbalanced arms, and 4.5% treatment-related deaths. Aggressive radiotherapy isn’t free: pneumonitis, forced pauses of the targeted pill, organ-specific risks.

How do I reconcile the pro camp with the con camp? By looking at who was in each trial. The positive trials: disease with few lesions, often dependent on a genetic driver, under a systemic treatment that’s working. The negative trial: the immunotherapy era, a different biology. My conclusion as a patient is not “everyone should be irradiated early”. It’s: if your disease is oligometastatic and systemically controlled, aggressive local consolidation has randomized data in its favor – and it’s worth asking for proactively, not waiting until something hurts.

But didn’t the last article say the opposite?

Attentive readers will notice the tension: two articles ago I wrote that assaults on the body – surgeries, trauma – can wake dormant cancer cells. Now I’m advocating aggressive local treatments. A contradiction?

No, and the difference is worth stating explicitly. One thing is elective trauma to healthy tissue, without cover – which sets off the body’s repair alarm without killing a single cancer cell. Another is the targeted destruction of tumor tissue, under the cover of an active systemic treatment patrolling the rest of the body. The first only sounds the alarm. The second empties the reservoir while the guard is on duty. Same body, same signals – but the balance sheet is the opposite.

The personal thread

At diagnosis, my spinal lesion was irradiated immediately, before starting the targeted pill. Months later, when the main lung tumor – metabolically melted, but not gone – started to flicker, I chose stereotactic radiotherapy on it, even though “it could have waited”. I can never know the counterfactual. But the strategy behind both decisions is exactly the one in this article: don’t let the reservoir exist just because it’s quiet.

What remains

Standard of care isn’t bad – it’s cautious, and the negative trials above show why the caution exists. But between “cautious” and “passive” there’s a difference the patient can influence. Depth of response matters. Every lesion eliminated is a resistance laboratory shut down. And the question “why are we waiting?” – asked politely, with these trials in hand – is one of the most valuable questions you can bring to a consultation.