PORTLAND — Maine’s insurance superintendent ruled Thursday that Blue Cross and Blue Shield must pay for the costly bone marrow transplant of a patient with advanced breast cancer.

The ruling by Joseph A. Edwards could affect other Maine women waiting to undergo the relatively new procedure which patients and their doctors see as their last chance for recovery.

Edwards determined that Blue Cross discriminated against Carole A. Poulin of Winslow last May when it refused to pay for her autologous bone marrow transplant on grounds that there was insufficient evidence to show that the treatment is effective against breast cancer.

Blue Cross previously had covered transplants of five Maine women in 1989, so it did not have sufficient grounds for denying Poulin coverage, Edwards said.

Blue Cross wants to review the written decision before deciding whether to appeal it in Superior Court, a Blue Cross official said.

Poulin, 47, had undergone a modified mastectomy and was told last spring she had 20 months to live without a transplant. When Blue Cross refused her coverage, she and her husband mortgaged their house and borrowed money from their business to make the $96,000 down payment for treatment at Duke University Medical Center in North Carolina.

Maine does not offer bone marrow transplants for breast cancer patients, but Maine Medical Center is considering such a program, said Dr. Kenneth A. Ault, an oncologist.

The treatment involves removing and freezing a patient’s bone marrow to prevent the immune system from being destroyed when a patient is given huge doses of cancer-fighting drugs.

Poulin, whose bill totaled $230,000, was discharged from the hospital in December and is now cancer-free and working full time.