Smoking and lung cancer

An important theme of the recent Conference on Retroviruses and Opportunistic Infections (CROI 2015) in Seattle, USA, was the impact of smoking on the health of people living with HIV. As HIV treatment has improved, it’s been shown that smoking doubles the risk of death for people living with HIV and actually causes more early deaths of HIV-positive people than HIV itself. These deaths are caused by lung cancer, other cancers, heart attacks, strokes and liver disease.

Smoking is the biggest risk factor for cancer

We already know that rates of many cancers are higher in people living with HIV than other people, and one study at the conference provided more evidence of this.

But why? There are several factors that contribute to cancer in people living with HIV:

  • Rates of smoking, drug use and alcohol use are higher in people living with HIV than the general population.
  • Hepatitis viruses and human papillomavirus (HPV) can contribute to some cancers, and rates of these are also higher in people living with HIV than the general population.
  • Weakened immune systems. (Some cancers, like non-Hodgkin’s lymphoma and Kaposi’s sarcoma are called ‘AIDS defining’ as they often occur when people living with HIV have a very low CD4 cell count.)
  • Continued inflammation and activation of the immune system over a period of years.

The conference heard that smoking is even more important than we previously thought. Researchers analysed cancer rates in over 39,000 people living with HIV. Specifically excluding those cancers which are AIDS-defining, almost 600 participants were diagnosed with a cancer during a ten-year period. The most common were lung cancer (101 people), anal cancer (96 people) and prostate cancer (60 people).

The researchers estimated how many of these cancers could be attributed to different risk factors. By far the most important factor was smoking – 37% of cancers would be avoided if people with HIV had the same rates of smoking as the general population. (Even if lung cancer were excluded, 29% of other cancers would be avoided if fewer people with HIV smoked.)

Other factors were less important. There would be 8% fewer cancers if people with HIV never had CD4 cell counts below 200 cells/mm3, 6% fewer if people never had AIDS, 4% fewer cancers if people never had a detectable viral load and 3% fewer if people with HIV had the same rate of hepatitis co-infection as the general population. But the study didn’t have good data on some other factors like alcohol use or HPV, so couldn’t estimate how important they were.

The researchers said that their study underlined how important it is for people with HIV to stop smoking and for doctors to find ways to help them to do so.

Helping people to quit

Another study looked at how effective the tablets varenicline (Champix) are in helping people with HIV stop smoking. Varenicline helps reduce craving for nicotine and dampens the pleasurable feelings associated with smoking. It has been available since 2006.

This is the first time it has been studied in people living with HIV, but research with HIV-negative people suggests that varenicline is more effective than the smoking cessation medication bupropion (Zyban), nicotine replacement products like patches or counselling on its own. Nonetheless, none of these – including varenicline – have been shown to work for more than a quarter of the people who use them.

That was also the finding of the study in people with HIV. It helped more of them to quit than a placebo dummy pill, but still only a minority managed to stop smoking.

Around 250 French people living with HIV took part in the study. Most were men in their forties who were doing well on HIV treatment. They had smoked for around 25 years, smoked around a packet a day, had tried to give up before and wanted to try again. They all received counselling to help them give up.

Almost a year later, of those who only had the counselling and a dummy pill, only 7% were not smoking. Results were better for those receiving the counselling and varenicline (at one stage a third had given up smoking), but after a year only 17% were not smoking.

Because of some concerns about side-effects, varenicline isn’t recommended for people with depression or anxiety.

Spotting lung cancer early

Finally, a study showed the benefit of using advanced techniques to screen for lung cancer early.

Lung cancer is one of the most difficult cancers to treat, especially because it is often diagnosed late. It can develop without noticeable symptoms and may have spread to other parts of the body by the time it is diagnosed.

But if lung cancer is diagnosed early, treatment is more likely to be successful. Treatment may be possible with surgery, rather than radiotherapy or chemotherapy.

Rather than a standard chest X-ray, the clinicians used computerised tomography (CT) scans. This uses X-rays to obtain a multiple-image scan of the entire chest, creating detailed images of the inside of the body. CT scans are more sensitive, picking up small, treatable tumours that are missed by standard X-rays. Research with HIV-negative people at high risk of lung cancer shows that screening with CT scans reduces deaths from lung cancer.

French clinicians wanted to see if screening with CT scans could help people living with HIV. Those screened smoked heavily or had smoked for many years. Of 442 people screened, 94 had unclear results or an abnormality that needed some follow-up. Lung cancer was ruled out for most participants, but ten people were diagnosed with lung cancer.

Importantly, six were diagnosed at an early, treatable stage. These cases are likely to have been missed if basic X-rays were used or screening didn’t happen at all. Also, most of the cases were in people in their forties and fifties, suggesting that screening shouldn’t only be reserved for older people.

In the UK, CT scans are currently only used after a standard X-ray has identified a problem. A leading cancer doctor has warned that delays introducing screening with CT scans could cost thousands of lives.