One of the best reports was on rats with prostate cancers in their shin bone (tibia). It showed that electroacupuncture of the point GB30 (Huantiao), decreased the levels of a couple of pain-producing chemical signals surrounding the spinal cord. This point is right above and tail-side of the hip joint. The chemical signals affected are preprodynorphin and dynorphin.
Full article: Some Science Behind Acupuncture for Cancer Pain