If you are interested in more of the history behind the different cancer treatments that we have today, "The Emperor of All Maladies: A Biography of Cancer" is a fantastic book about it. Probably my favourite book of all time, a lot of parallels with the themes in this article about prevention being a huge contributor, and how recently we've had some success in very targeted cancer drugs.
If someone wants a different take on why cancer treatment has progressed very slowly, there is "Cancer, Incorporated" by Ralph Moss.
I'm sure there are some instances where drugs to treat very rare cancers were not entered into trials because the company didn't think it was profitable - the book actually lays out one of the examples of this. But that isn't really relevant to the overall fight against cancer. The reality is that we have limited resources to develop and test new drugs, and how profitable a new cancer drug will be is a somewhat reasonable proxy for how important it is to develop.