he new findings were presented in a poster here at the 32nd Annual San Antonio Breast Cancer Symposium by George Perkins, MD, from the Department of Radiation Oncology at the University of Texas M.D. Anderson Cancer center in Houston.
"While mucinous breast cancer is thought to be a disease with a favorable prognosis, our study is the first to identify it as one associated with significant multifocal presentation, which is a potentially unfavorable aspect," he said.
"In recent years, there has been an overall trend toward minimization of treatment for women with this subtype, because these mucinous tumors are considered to have an extremely favorable prognosis," Dr. Perkins explained in an interview. In particular, there has been a trend away from using whole-breast irradiation in these patients, so some patients receive no radiation at all, whereas others are treated with partial breast irradiation, he explained.
"Our study shows that that about one third of these women have more than a solitary lesion. This disease may be more multicentric than previously thought, and this is the first time that this has been reported," he said. These new findings suggest that undertreatment may be a "significant hazard for patients," he added.
It is important that the pendulum does not swing too far.
"You have to be very careful about offering no treatment or minimized treatment," he said. "In an era where there is a concern about overtreatment, it is important that the pendulum does not swing too far so that we are undertreating."
Claudine Issacs, MD, director of the Clinical Breast Cancer Program at the Georgetown Lombardi Comprehensive Cancer Center in Washington, DC, who moderated a press conference at which the findings were highlighted, added: "Partial-breast irradiation is an investigational treatment and should not be offered as a standard of care."
Large Series of Rare Tumor Type
Mucinous tumors are diagnosed in about 2% of all breast cancer patients, but they are more common in older women. This subtype is found in about 8% to 10% of women 70 or years or older, but in fewer than 0.5% of those 35 years or younger.
The M.D. Anderson team reviewed the charts of 264 patients diagnosed with a pure mucinous carcinoma from 1965 to 2005; the median age was 57 years, and median follow-up was 14 years. "This is one of the largest single-institution experiences with a relatively uncommon subtype, and it has a significant long-term follow-up of patients," Dr. Perkins said.
The favorable prognosis is apparent from the long-term follow-up, as shown in the table below.
Outcome After Long-Term Follow-Up
| Outcome | 5 Years | 10 Years | 15 Years |
| Overall survival rate (%) | 95 | 97 | 97 |
| Distant metastases-free survival rate (9%) | 88 | 95 | 94 |
| Local regional control rate (%) | 83 | 92 | 85 |
On initial examination, only 10% of these women had a multicentric/multifocal presentation. However, a detailed pathology review revealed a 38% rate of multicentric/multifocal disease after resection, which surprised the team, Dr. Perkins explained.
"We had previously been surprised by the decreasing age at presentation in this population, and by the regression of favorable outcomes toward the lower outcomes of other common breast cancer subtypes over time," he explained in a statement. "This reinforces our commitment to interdisciplinary care and true personalized patient treatment in this variant," he said.
There needs to be a move away from "the assumption that it may not matter which treatment approach is taken because this is a favorable disease," he added.
32nd Annual San Antonio Breast Cancer Symposium (SABCS): Abstract 4117. Presented December 12, 2009.
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