Median survival time from cancer diagnosis

The BBC has a story about median survival times from diagnosis for various cancers, and how they have changed in the last 40 years.  For some cancers there's been a big improvement, for others there isn't.  A spokeswoman for Cancer Research UK says that more research is urgently needed into cancers for which there has been little improvement.

The source is a research briefing paper by Macmillan Cancer Support.  Under the heading "Shocking Variation" the introduction says:

First the good news: overall median survival time for all cancer types 40 years ago was just one year, now it is predicted to be nearly six years. This improvement is testament to the improvements in surgery, diagnosis, radiotherapy, and new drugs. There have been particularly dramatic improvements in survival time for breast cancer, colon cancer and Non-Hodgkin’s Lymphoma – with many years added to median survival times.
But the good news is tempered by the woeful lack of improvement in other cancers. There has been almost no progress for cancers like lung and brain, where median survival times have risen by mere weeks. Shockingly pancreatic cancer median survival time has hardly risen at all. The NHS and cancer community must urgently look at why.

Apart from not being shocked, I don't disagree with that.  But there is something important left unsaid.  There are three ways to improve cancer survival time from diagnosis.
1) Better treatments
2) Earlier diagnosis, even if the treatment is ineffective
3) More effective treatment made possible by earlier diagnosis

Certainly treatments have got better for all cancers - medical science is a wonderful thing.  But there are few in which this has given us a really big increase in median survival time: Non-Hodgkin's Lymphoma is one.  I suspect that most of the improvement has been from much earlier diagnosis made possible by scanning technology invented in the early 70s, by endoscopy, and by testing for tumour markers such as PSA.  And it is hard to separate effects (2) and (3).

Screening programmes are likely to become widely deployed only if there is evidence that they decrease mortality: that suggests that treatment following early diagnosis reduces mortality even in asymptomatic patients, but it doesn't tell us by how much it increases median survival.  (There's a helpful discussion of how to evaluate screening programmes here.)

The Macmillan report notes that the prostate cancer should be treated with caution because of the increased "incidence" of low grade tumours following the introduction of PSA testing (they should say "diagnosis").  Similar caution should be applied to interpreting the data for all cancers.