You have just been diagnosed with cancer. You still smoke. The shame, the fear, the need to breathe make you hit the cigarette harder than before. It is a human reaction, and you are neither weak nor stupid for it.

But there is a truth you are not always told clearly enough: keeping on smoking during your treatment lowers your chances that the treatment will work. And quitting, even late, concretely changes your probability of recovery.

Why tobacco sabotages your treatment

Several documented mechanisms stack up:

• Hypoxia: carbon monoxide reduces oxygen in your tissues. And radiotherapy needs oxygen to kill tumour cells (the "radiosensitiser" effect).

• Altered metabolism: smoke modifies certain liver enzymes, which changes how your body handles chemo — often by raising its toxicity.

• Weakened immunity: fewer natural killer cells in circulation, which are precisely the cells that help clear cancer cells.

• Chronic inflammation: the inflammatory terrain favours tumour progression and treatment resistance.

Radiotherapy: the best-documented scenario

It is on radiotherapy that the evidence is strongest. A recent meta-analysis finds, in active smokers during treatment:

• +56% risk of locoregional recurrence (radiotherapy alone),

• × 4.28 risk of recurrence in chemoradiotherapy,

• +88% risk of poor disease-free survival,

• +84% risk of severe skin and mucosal toxicity.

For head-and-neck and breast cancers in particular, thresholds have been integrated into clinical protocols: 10 pack-years is a pivotal value in head-and-neck oncology.

Chemotherapy: less evidence, but not zero

The effect of tobacco on chemotherapy efficacy is less clear than for radiotherapy — studies are more contradictory. But what is documented:

• liver toxicity is worse in smokers,

• post-chemo respiratory complications are more frequent,

• fatigue and recovery between cycles are harder.

The immunotherapy case: why it is different

For checkpoint inhibitors (anti-PD-1, anti-PD-L1), the literature shows that smokers paradoxically have a better response. Why? Because cancers in smokers often carry more mutations, hence more antigens the immune system can recognise.

And second cancers?

Continuing to smoke after a first cancer multiplies your risk of developing a second — including in locations not commonly associated with tobacco (breast, lymphoma, testicle). Patients treated with radiotherapy for breast cancer who keep smoking see their risk of myocardial infarction multiplied by 3 in the following years.

How to go about it, without guilt

A cancer diagnosis is a period of emotional chaos. The cigarette, in that moment, is not just an addiction — it is also a marker, a lifeline, a familiar ritual in a life that is tipping over.

A few useful principles:

• Ask for medical help from the start. Many cancer centres have tobacco-cessation consultations. Nicotine substitutes are safe during treatment.

• Do not set yourself a perfect quit. Cutting in half is already measurable gain.

• Do not use shame as a driver. It will make you smoke more, not less.

• Consider vaping. As a transition, it is validated by several professional societies, including in oncology.

In United Kingdom

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