Actually they do publish most of the results, it's just negative results don't usually generate lots of press. With cancer patients it's typically late stage cancer patients on clinical trials, many/most of which die regardless of the treatment. A very positive treatment can be on the order of a few months of increased overall survivability on average. Typically this means some patients get a very positive result but most patients have so results either because they aren't a good match for the treatment or are too damaged to live longer anyways due to comorbidities. Unless you're constant following the studies you're unlikely to see the negative results.