We preview tomorrow night's American Experience documentary "The Cancer Detectives" with co-directors/ co-producers Amanda Pollak and Gene Tempest. The film tells the story of the development of the pap smear, an essential tool for early cancer detection in women. The test is named for Dr. George Papanicolaou and his wife Andromichi, who was his faithful lab assistant for decades. As one guest in the film states, "science is so often about incidental, lucky accidents" - and this particular innovation is a perfect example of that.