12 August 2026

Why does cancer progress for some while for others the disease remains dormant?

Brenda was one of those patients who has stayed in my memory. She had a wry sense of humour with which she shooed away any misfortune that might come a-calling. Community-minded and neighbourly, she was widely liked in the Somerset town where I practised.

Eighteen years ago, when in her early sixties, she came to see me with backache. The pain was right between the shoulder blades and had come on inexplicably. “It couldn’t be that blessed cancer is back, could it?” I had a sudden inkling of the shadowy threat she had lived with for the decade since her mastectomy.

As it turned out it wasn’t just in the bone; she had metastatic deposits on her liver and lungs. She bore radio- and chemotherapy stoically but before long I was supporting her husband in his bereavement. I remember the difficulty I had in comprehending how the cancer that had lain silent for so very long could so suddenly and aggressively re-emerge.

Understanding of cancer biology has advanced dramatically in the years since. The old idea – that, since metastatic spread comes late in a tumour’s evolution, if the primary tumour is caught early it should lead to a cure – is largely wrong. In many cases, metastatic disease has disseminated long before the primary tumour is even detectable. And the reasons it can take years to manifest – and why in some people it never will – is opening new ways of approaching post-cancer care.

It has long been known that cancer metastasis is a very inefficient process: injecting laboratory animals with hundreds of thousands of malignant cells might only result in a scattering of viable deposits. These rapaciously potent cells appear unable to survive just anywhere; they need to lodge in “niches”, highly specific micro-environments in organs such as bone, lung or liver that ordinarily house and regulate special cells capable of generating new tissues. Once it occupies one of these niches, the cancer cell lies quiescent, not dividing at all – a dormant cancer cell (DCC).

This dormancy is far from a passive process. The DCC disguises itself to “hide” from the immune system, which constantly patrols niche sites on the lookout for trouble. And while dormant, it develops genetic capacities – resistance to certain drugs, the ability to stimulate new blood vessel formation, or to further evade immune system control. But while the DCC might be utilising this often years-long residency, it is less a lodging arrangement and more one of custody. The specialised cells that comprise the niche micro-environment suppress the DCC from dividing so that no new tumour will grow. The impasse will endure until something upsets the uneasy equilibrium.

Recent research – stimulated by the excess cancer death rates seen in the years following the pandemic – has shown that infection with Covid or influenza will trigger metastatic growth from lung DCCs in a mouse model. The surge in inflammatory chemicals caused by these viral infections enables the DCCs to escape from the suppression of the niche micro-environment. And we know that certain drugs or non-cancerous conditions that influence the rate of natural bone turnover either reduce or increase the chance of skeletal metastases forming from DCCs in bone niches.

Cancer is an often deadly foe that can defy all efforts at control, but our knowledge of its behaviour has been built on tragic cases like Brenda’s. We know very little about those whose dormant disease never progresses: what might they teach us about optimal cancer aftercare? Chronic stress has been shown to have a role in dormancy breakdown but, as yet, there is no clear evidence that stress-reduction techniques are protective. Exercise has a robust evidence base – regular aerobic training has been shown to reduce risk of metastases in some cancer survivors by up to 70 per cent. Better understanding of cancer biology will generate new treatments, I’m sure, but it also illustrates that trying our best to ensure healthy bodily function is an important cancer care goal.

[Further reading: Frank Cottrell-Boyce’s canon for children]