In an article seen at Genetic Engineering & Biotechnology News, called "Shrinking Tumors with Injections of Engineered Bacteria" in April 2014, bacteria use to destroy tumor cells was the topic in review.
Despite the fact that tumor growth of any form and treatments for their management, result in a low immune system has been known for decades, in 1890, a scientist proposed a tumor treatment which would use a combination of bacteria to kill tumors. The idea was rejected by the medical community at that point in time, but has been since in review again.
A Trial has recently confirming that tumors cells, which are also referred to as neoplasm tissue, can in fact be killed with the right bacteria combinations with a chance of not harming healthy tissue. Bacteria chosen for this trial are bacteria that only survive in oxygen-poor environments, which would allow them to live and thrive while killing cells deep within tumors. Not only would this mean that if injected directly into a tumor it would destroy the tumor only, but it would also seek tumors out if given to an individual any other way.
Research of this method has not extended past animals at this time with the exception of one patient. So far the side effects seen for this treatment has been limited to simply bacterial infection issues.
How long it will take for this research to extend to different causes for tumors cannot be guessed. Will it matter how much tumor mass to body mass an individual might have? As always research developments always lead to more questions and more research is needed.