Lung cancer – a smoker’s disease?

In July 2013, Harpal Kumar, the head of Cancer Research UK said, “It is not so long ago that we used to say more than nine in ten lung-cancers were smoking-related, and now we say eight in ten”.  In the US, 17.5% of lung cancers occur in patients who have never smoked.  If non-smokers lung cancer were counted as a different disease, it would still be the 7th most common cause of cancer death worldwide.

However, lung cancer for non-smokers is a very different disease to that of smokers.  According to Paul Paik from the Memorial Sloan-Kettering Cancer Centre in New York, people who have never smoked survive for approximately twice as long as people who have previously smoked or still do smoke.  He says this is because “never-smokers seem to have more good-prognosis mutations”.  This means that never-smokers have fewer mutations in their cancerous cells, so they tend to only have one or two bad mutations rather than hundreds for smokers.  Hence non-smokers are easier to treat because cancer specific drugs can be used to target the cancer more directly.

Targeted drugs work by tackling specific mutations within the lung cancer on only one or two genes, which is why they are more effective at treating non-smoker cancer: there aren’t as many mutations to target.  This treatment requires biopsies to be taken and the DNA of the cancer to be sequenced to find the mutations.  Targeted drugs are used to tackle common mutations but in the future it may be possible to create personalised drugs specific to that person’s cancer.  Examples of current targeted drugs include erlotinib (Taraceva) which targets mutations on the EGFT gene and crizotinibl (Xalkori) which targets mutations on the ALK gene.

Patients treated with these targeted drugs usually find that their cancers come back, so the drug doesn’t usually cure the patient of the cancer, but it can extend their life expectancy.  Targeted drugs usually increase life expectancies by over 1.5 years.  Lung cancer is in the top 10 killers worldwide.  With an annual death toll of 1.5 million it accounts for 2.7% of world deaths.

In the UK more people die of lung cancer than of colon, prostate and breast cancer combined, with 35,000 deaths per year and a 90% death rate.  In the UK 12% of these deaths aren’t smoking related:  that’s over 4,000 deaths per year.  Risk factors other than active and passive smoking include age:  80% of lung cancer cases occur in people over 60.

Lung cancer patients shouldn’t be targeted for lower quality care because of the stigma associated with smoking.  Although most patients are smokers, non-smokers lung cancer is on the rise, and with an increase in life expectancies the risks of developing this disease increases with an ageing population.

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