I just finished reading J. Craig Venter's book Life at the Speed of Light: From the Double Helix to the Dawn of Digital Life. The book is a little over a year old now, and Venter has an optimistic outlook that bacteriophage therapy will become an effective alternative to gene therapy and viral immunotherapy. He mentioned that the JCVI (J. Craig Venter Institute) is working on such projects. Are other companies also researching, and has progress been made? What are the expected risks? How can rogue, harmful phage mutations be controlled? Can this type of therapy be applied to cancers?
The Eliava Institute in Tiflis (Georgia (a country)) has been at it since the 1930`s. A US company sells a phageproduct for desinfection of meat.
The risk of Phagetherapy is there, if the phage is ill choosen or contaminated with other phage it could introduce pathogenic genes to the target or other bacteria.
If those risks are eliminated there is very little risk in phage therapy aside from the fact that it may not work at all. Phagetherapy is most useful in regions where bacteria are normally found, in other places the immunesystem will make short work of it.
The faster and cheaper sequencing gets the more effective phagetherapy will become. Since a "bad" bacteria can quickly be isolated and a proper "phage cocktail" can be prepared. If we get to the point that we can sequence the whole microbiom of a person then i bet that Phagetherapy will be a very normal thing.
To your cancer question, i think its rather hard to apply it to cancer therapy except if u are looking to combat the cancer with a Intracellular bacteria...but then again. How u get the phage to it.
A excellent read on this topic is the Book "the bacteriophages".
You run the risk of the killed cells suddenly releasing huge quantities of cytokines. If this occurs you may cause spike in capillary permeability and basically create massive sepsis. The bacteria will have to be killed SLOWLY to prevent them spilling their contents into the circulatory system. But, I have always believed phages could be engineered to control certain infections like urosepsis. But, any phage therapy may be single use only. I used to inject them into rabbits to prepare antisera used in phage growth experiments, I guess that is one of the reasons phage therapy is out of the mainstream. http://www.nature.com/news/phage-therapy-gets-revitalized-1.15348