A 66-year-old Houston woman's golf ball-sized breast tumor is now almost invisible to the naked eye after only four rounds of an investigational drug regimen.

Dr. Jenny Chang, director of the Methodist Cancer Center and breast medical oncologist, said the results are promising but no conclusions can be made because this is an ongoing study and the patient is the first at Methodist to be enrolled.

The Rev. Noel Denison, a retired Methodist minister, was diagnosed with locally advanced HER2-positive breast cancer and is enrolled in the study at Methodist, one of only two locations in the United States. The clinical trial is for locally advanced or metastatic HER2-positive breast cancer and combines standard chemotherapy with trastuzumab emtansine, better known in the breast cancer world as T-DM1, and pertuzumab, a monoclonal antibody that also attaches to HER2 on cancer cells.

T-DM1 is in a new class of cancer-fighting agents called antibody drug conjugates. By combining the antibody trastuzumab directly with docetaxel (standard chemotherapy) and/or pertuzumab, the T-DMI is designed to attack the tumor cells directly and deliver the chemotherapy.

"Women with HER2-positive breast cancer now have a lot of opportunities for treatment," said Chang, the study's principal investigator at Methodist. "Trastuzumab, commonly known as herceptin, is good, but we're hopeful that this combination we're using, known as a super herceptin, is even better at targeting and killing the cancer cells."

Study patients receive T-DM1 and docetaxel on day 1 of each 3-week cycle (up to six cycles). For patients with locally advanced breast cancer, pertuzumab may be added to T-DM1 and docetaxel. Sold as Perjeta, pertuzumab is an FDA-approved drug used in combination with herceptin and docetaxel to treat certain patients with HER2-positive metastatic breast cancer.

Previous research involving more than 1,000 women with advanced HER-2 breast cancer showed T-DM1 caused fewer and less harsh side effects than current standard treatment.

Five months after her initial diagnosis, Denison is still undergoing the experimental regimen, but she is back to the things she loves -- gardening, volunteering in her community and spending time with her grandchildren.

"I'm also putting my time and energy into breast cancer education," Denison said. "I live with the pay it forward attitude. The Methodist Cancer Center gave so much to me; it is only fitting to give back to others in need."

Genentech Inc./F. Hoffmann La Roche Ltd. is funding this clinical trial.