Hacker News Reader

Comment by scottlamb | Hacker News Reader

> However, despite the high false positive rate, breast cancer screening is a net beneficial procedure (though not without controversy) in that when applied in a population, long term outcomes like mortality improve.

I've read that's also a statistically tricky statement. IIRC, they measure survival time from when the cancer was detected. So early detection by definition improves the survival stats even when there's no meaningful treatment.

If I've read about this, I'm sure medical practitioners are well aware of it, but even so, I don't think it's easy to correct for it. How do you determine when a late-detected cancer actually started?

View on HN

You don't, you just measure long term outcomes like mortality in a treatment and control arm. Potentially you have to use a synthetic control.

I am most familiar with NLST which actually was a long term randomized trial.

Thanks! Paraphrasing to check my understanding: you don't use the stat I mentioned, instead measuring whether the patients ultimately die from cancer or something else. You use a control, so after like detection method some patients get treated and some don't. But not treating may be unethical, so you use a "synthetic control", which I had to look up. Basically an invented group of not-treated patients based on statistics from other populations. [0] It sounds interesting but tricky to get right. "A healthy degree of scepticism on the use of synthetic controls is thus expected from the scientific community."

[edit: or, looking at the NLST you mentioned [1], maybe "treatment" doesn't always mean what I think of as treatment. They are actually comparing two different detection methods, and they aren't using a synthetic control.]

Do they ever use the "survival time after detection" stat I mentioned anymore, or has it been (/ should it be) abandoned?

[0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7218288/

[1] https://www.cancer.gov/types/lung/research/nlst

Nice follow up!

Yes, NLST was actually a real randomized control trial for lung cancer screening, done before it was known whether or not it was helpful. The trial eventually stopped once they had enough outcome based evidence.

The statistic you mentioned is not used in assessing the effectiveness of screening. It does closely relate to what is though to be the causal mechanism that leads to effectiveness.

Reply on news.ycombinator.com