ORLANDO, Fla.  The breast cancer drug Herceptin may now have a role in treating stomach cancer as well, according to study results announced here on Sunday at the annual meeting of the American Society of Clinical Oncology.

Scientists also announced that a new class of drugs called PARP inhibitors has shown promise against hard-to-treat forms of breast cancer and that a cancer vaccine for non-Hodgkin’s lymphoma that struck out twice might have succeeded on a third try.

In a study sponsored by Roche, which sells Herceptin, stomach cancer patients who received Herceptin in addition to standard chemotherapy lived a median of 13.8 months compared with 11.1 months for those who treated with standard chemotherapy alone.

Herceptin is used to treat the roughly 20 percent of women whose breast tumors have an abundance of a protein called Her2. In the new study, doctors found that 22 percent of 3,807 patients with metastatic stomach cancer also had high amounts of Her2 in their tumors. The study involved 594 of those Her2-positive patients.