And it's when he talks about the subject of his 147th paper, published in the journal Science two weeks ago, that this 44-year-old's face really lights up.
Hailed as one of the biggest breakthroughs in cancer research for decades, Professor Swanton and his team identified the "Achilles' heel" of cancer that could potentially harness the patient's own immune system to create new bespoke treatments for advanced or returning cancers.
Essentially, they found that cancers hold within them the seeds of their own destruction because they all carry "flags" which can be spotted by the immune system, no matter how much they mutate (and cancers mutate often and quickly).
This pioneering discovery now paves the way for a new way of treating cancer by using the patient's own immune cells, grown in the lab and re-administered for individualised treatment. For a disease that still takes the lives of 163,400 Britons each year, this is as exciting as it gets.
The problem - cancer drug resistance
Just last week, it was revealed that scientists had built nanoparticle factories that acted as "Trojan horse" vessels which, once injected, could ferry chemotherapy drugs direct to cancers.
In separate research on 257 women, scientists showed that two drugs, lapatinib and trastuzumab, when used together could shrink or even eliminate breast cancer tumours in less than two weeks.
However, while exciting new research continues, and over the past 40 years survival rates have doubled, many cancers remain incurable.
The reason current treatments are often unsuccessful is because cancer evolves and mutates rapidly, tricking the immune system and the drugs being administered to treat it.
For example, a drug such as Herceptin, used to treat the 15-25 per cent of women with breast cancer who have HER-2 positive cancers, targets some tumour cells, but can still leave behind a reservoir of cells that can potentially grow and become resistant to treatment.
The same problem of drug resistance occurs with most such cancer drugs, known as "targeted therapies".
"It's very like bacterial resistance," says Professor Swanton. "When you give an antibiotic, bacteria develop resistance. When you give a chemotherapy drug, cancers develop resistance and stop responding to them."
The potential solution - the body's own immune cells
Prof Swanton's team, based at the Crick Institute and University College London and funded by Cancer Research UK, found that even when it had mutated, a cancer still carried signature molecules that didn't change and could be spotted by the immune system's disease-fighting T-cells.
"As cancers evolve, they develop mutations and these mutations can, in some cases, be seen as flags on the surface of the tumour cells by the immune system as being abnormal and so the immune system will try to tackle those flags," says Prof Swanton.
His team took numerous biopsies from two patients with lung cancer and found evidence that their immune systems recognised the flags on the surface of every tumour cell.
"I hope this is a breakthrough, but we won't know until we have treated the first patient," says Prof Swanton, who specialises in lung cancer, which kills 45,000 people a year.
"Around 85 per cent of the patients I see present with advanced disease and we will not be able to cure them - that is something we have to get to grips with."
The future vision - individualised cancer therapies
Though preliminary, the potential of such a discovery is momentous.
"Because no two tumours are the same, we want to find a way to hit those flag proteins by using the body's own defences to do it individually for each patient."
Theoretically, this means oncologists could look at the genetic profile of a tumour and locate the "flags" that are recognised by an individual's immune system, then engineer billions of these special immune T-cells and transfer them back into the patient "so they have more of their own immune cells to fight their own cancers", says Prof Swanton.
The first safety trials could happen within two years, followed potentially by the treatments of the first patients (though it could take 10-15 years before such treatment became routine therapy). It's ambitious, he says, but important because the one-size-fits-all approach we currently have is flawed because drug resistance will always occur in some patients.
The findings could also be used to create a vaccine to increase the body's defences. "In this scenario, which is probably a more likely one, we would take the flags themselves (the common genetic mutations) and inject them back into the patient in small amounts to get the body's own defences fighting against the cancer."
Not a cure - yet
Prof Swanton is adamant "this is not a cure, though we hope it might have the potential to improve outcomes", and, his peers hope, offer a totally new way of treating cancer.
"It gives us vital clues about how to specifically tailor treatment for a patient using their own immune system," says Prof Peter Johnson, Cancer Research UK's lead clinician, "as well as filling in gaps in our knowledge and giving us hope of developing better treatments for cancers we have previously found hardest to treat."
Cancer cure: A timeline
1923 Radiotherapy first used to treat cervical cancer
1954 Proof of a link between smoking and lung cancer first published
1956 First chemotherapy drug used to treat a rare tumour
1963 Discovery of first human cancer virus
1972 Drug for testicular cancer developed
1994-95 The first breast cancer genes BRAC-1 and BRAC-2 discovered.
2011 International Cancer Genome Consortium formed to map the genetic faults behind 50 types of cancer
2013 Trial finds taking the drug anastrozole daily can halve the risk of breast cancer in older women
2016 Scientists build nanoparticles that act as "Trojan horse" vessels to ferry chemotherapy drugs direct to cancers
