The two federally-designated cancer centers in the Boston area are embarking on an unusual alliance that will combine the different research strengths of both organizations to yield new treatments and insights into two highly lethal cancers. Researchers at the David H. Koch Institute for Integrative Cancer Research at MIT and the Dana-Farber/Harvard Cancer Center have collaborated in the past, but the so-called “bridge’’ project being unveiled today is intended to spark increased cross-Charles teamwork.