# If smoking causes lung cancer, why has a decline in smoking not led to a decline in lung cancer?

According to the CDC, smoking prevalence among US adults (18+) has decreased quite a bit over the years:

1974: 37.1% of the population
1980: 33.2
1990: 25.5
2000: 23.3
2010: 19.3


According to cancer.gov the rates of new cases of lung cancer in the US haven't consistently gone down over the years:

1975: 52.5/100,000 people
1980: 60.7
1990: 68.1
2000: 64.1
2010: 57.3


If smoking causes lung cancer - according to the CDC "cigarette smoking is linked to about 90% of lung cancers" - shouldn't such a clear decline in the number of smokers have also caused a clear decline in the incidence of lung cancer? How have experts/doctors/medical scientists/etc. addressed these statistics, if at all?

• @PedroWerneck Would you be able to identify for me the page number (or chapter title) in which he analyses this contradiction in detail, or an accurately/directly-quoted sentence fragment I can search for to find the place you're referring to in the book? – ChrisW Dec 4 '14 at 15:54
• @PedroWerneck It criticizes (i.e. quotes people who identify possible methodlogical faults/concerns with) epidemiology. Although "many other contradictions are analysed in detail" I didn't notice that it analyzes 'lag', at all, anywhere. – ChrisW Dec 4 '14 at 17:02
• "I'm not here for arguing." Fooled me. – Andrew Lazarus Dec 4 '14 at 19:16
• Lol, really? "This is analyzed in this book" "Which part of the book?" "Chapter 2" "I checked and no it doesn't" "Well go read it all then!" Come on dude.. – Claudiu Dec 4 '14 at 23:38
• Consider that in 1975 and 1980 more people died without having been diagnosed with cancer than later years. Throw those two years out and a decline emerges. Our ability to detect cancer has increased over time, and if not accounted for would throw such statistics off. My grandmother was a 2 pack a day smoker for 70 years of her life, and in her late 90's after dementia set in a mass was detected but no further diagnosis was made as family elected for hospice care rather than cancer treatment. No treatment means she isn't included in cancer stats. – Adam Davis Dec 5 '14 at 0:45

The cancer.gov site you referenced says that the median age of diagnosis is 70. That implies that you smoke and then, later in life/time, you may be diagnosed with cancer.

Therefore, for example, Lung cancer incidence statistics from the UK says:

Trends in lung cancer incidence rates reflect past trends in cigarette smoking prevalence. Smoking rates peaked earlier in males than in females, so lung cancer rates in men have been decreasing for some decades, but this decrease is yet to start in women.

Figure 1.2 in your cancer.gov report shows that cancer rates for all people have been decreasing steadily, since 1992, and since 1986 for men.

• This cancer.gov page says the same thing, i.e. that there's "lag": cancer.gov/researchandfunding/snapshots/lung – ChrisW Dec 4 '14 at 5:15
• When you research it, you'd be most welcome to write/post an answer of your own to this question. – ChrisW Dec 4 '14 at 5:35
• It might be a good addition to mention that the preferred CT screening is used much more frequently now than it was prior to the 1990s. It may not be that incidences of cancer were rising until the mid-90s, but our detection of them was. – Is Begot Dec 4 '14 at 14:24
• @Geobits Is that so? Instead wouldn't that effect be negligible, because if you develop lung cancer then it's impossible to avoid detecting it (because you die of it) within relatively few years? OTOH life expectancy has increased since 1975, maybe that (longer life) increases (late-in-life) prevalence of cancer. – ChrisW Dec 4 '14 at 14:36
• @Geobits Or you die because of heart attack due to long-term lack of oxygen, and you're never diagnosed. Or you die from "flu" which is unrecognized pneumonia that is more common and more severe if you get lungs cancer. Ad nobody cares what it was once you're dead. And so on and so forth. As well, what you mention, we get old enough now to develop various diseases that likely didn't exist before (because we were simply dying too young). There are too many factors here that increase the rate in which many diseases appear. That's why one has to be really careful in statistic epidemiology. – yo' Dec 5 '14 at 11:22

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