Recurrence and Survival in the American Society of Breast Surgeons (ASBS) MammoSite RTS Registry Trial

Reviewer: Christine Hill, MD
Abramson Cancer Center of the University of Pennsylvania
Ultima Vez Modificado: 22 de septiembre del 2008

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Presenter: P.D. Beitsch
Presenter's Affiliation: American Society of Breast Surgeons, Dallas, TX
Type of Session: Scientific

Background

  • Large trials examining outcomes for early-stage breast cancer patients have demonstrated that lumpectomy followed by radiotherapy is equivalent to mastectomy.
  • Local recurrence rates remain higher for patients treated with breast conservation therapy (lumpectomy plus radiotherapy) (BCT); however, overall survival rates are equivalent for the two treatments (Fiser B, NEJM, 2002). 
  • Patients treated with BCT have historically received radiation to the entire breast followed by a boost to the tumor bed. This boost may be delivered using photons, electrons, or radioactive implant.
  • Recently, several centers have initiated use of techniques delivering radiotherapy only to the tumor bed after lumpectomy, rather than the whole breast; this method of treatment is globally referred to as partial breast irradiation (PBI).
  • The MammoSite® Radiation Therapy System (RTS) has been developed in efforts to deliver radiotherapeutic dose to tumor bed and the region surrounding it. 
    • Patients undergoing treatment with MammoSite® RTS undergo placement of the MammoSite® balloon into the lumpectomy cavity at the time of lumpectomy.
    • Following this, high-dose rate brachytherapy is delivered via the balloon to the lumpectomy category twice daily, over 5 days.
    • After radiotherapy is completed, the MammoSite® balloon is removed.
  • The Mammosite® RTS was FDA approved for treatment of early-stage breast cancer in May, 2002. At that time, the Mammosite® RTS Registry Trial was begun; its control was assumed by the American Society of Breast Surgeons (ASBS) in November, 2002.
  • Recommended patient eligibility requirements include age of at least 45 years, small tumor size, negative surgical margins, and a distance of at least 7 mm from the lumpectomy cavity to the skin surface.
  • Over the 6 years during which Mammosite® RTS technology has been employed, several centers have reported local recurrence rates and overall survival; however, to date, these trials have analyzed small numbers of patients at single institutions.
  • The study presented here reports outcomes data from the ASBS Mammosite® RTS Registry Trial.

Materials and Methods

  • Patients were enrolled on the registry from 97 different institutions, and received care from 121 different physicians.
  • A total of 1440 women were treated with Mammosite® RTS technology from May, 2002 until September, 2004. Among these women, 9 had bilateral tumors both treated with Mammosite® RTS. A total of 1449 tumors were thus analyzed.
  • Ipsilateral breast tumor recurrences (IBTR), regional recurrences, and survival were evaluated.
  • Potential contributing factors to disease recurrence, including margin status, nodal status, tumor location, tumor histology, breast size, and tumor size were analyzed.

Results

  • Of the women who received this treatment, the median age was 65 years (range 32 – 94 years).
  • Of the 1449 cases analyzed, 1255 cases represented invasive ductal carcinoma, and 194 cases ductal carcinoma in situ (DCIS).
    • Median tumor size was 1 cm (range 0.1 – 4.5 cm).
    • Tumors were stage Tis in 13% of cases, T1A in 11% of cases, T1B in 35% of cases, T1C in 35% of cases, and T2 in 6% of cases.
  • Surgical margins were negative in 91% of cases, close in 8% of cases, and positive in 1% of cases.
  • Axillary nodal status was negative in 83% of cases, and positive in 3% of cases. Axillary nodal status was not examined in 14% of cases, all of which represented DCIS.
  • Approximately half (53%) of patients received hormonal treatments. Chemotherapy was received by 6% of patients.
  • Median follow up was 42 months.
  • Of 1449 cases, 27 IBTR were observed. Of these, 9 were in the region of the tumor bed, and 18 elsewhere in the ipsilateral breast. The 3-year actuarial IBTR rate was 2.15%.
  • Axillary recurrences were observed in 3 cases (0.26%).
  • Contralateral disease developed in 11 cases (0.74%).
  • Distant disease developed in 16 cases (1.23%).
  • Three-year actuarial overall survival was 95.6%. Cancer-specific survival was 99.2%.
  • The first 400 Mammosite® RTS cases were examined in a separate analysis.
    • Median follow-up was 52 months.
    • In-breast tumor recurrence occurred in 8 cases, 2 within the tumor bed, and 6 elsewhere in the ipsilateral breast. The 4-year actuarial IBTR rate was 2.65%.
    • Of this subset, one patient developed an axillary recurrence (0.27%), 6 failed distantly (2.16%), and 2 developed contralateral disease (0.44%). 
    • Overall 4-year actuarial survival was 93.1%, with disease free survival of 88.9% and cancer-specific survival of 99.6%
  • . Margin status (positive vs. negative), nodal status, tumor location, histology, histologic grade, extensive intraductal component, age (< 45 vs. 45+), tumor size (< 2 cm vs 2 cm+), breast size, Mammosite® balloon placement technique, Tamoxifen use, and chemotherapy use were examined for association with IBTR.
  • None of the potential contributing factors were statistically significant; however, impact of extensive intraductal component, non-use of Tamoxifen, and high histologic grade trended towards significance in increasing risk of IBTR (p = 0.07, p = 0.09, and p = 0.10, respectively).

Author's Conclusions

  • The authors conclude that PBI with Mammosite® RTS results in low rates of IBTR and axillary recurrence, and acceptable cancer specific survival.
  • They note that the first 400 consecutive cases, with 5 years of follow-up, had equivalent recurrence rates as the group as a whole.
  • They describe similar associations with increased risk of IBRT, such as extensive intraductal component, non-use of Tamoxifen, and high histologic grade as have been noted in previous studies.

Clinical/Scientific Implications

  • The Mammosite® RTS and PBI in general have gained popularity among clinicians and patients over the recent decade.
  • As the authors point out, most reports have included relatively small numbers of patients, and this study represents an important contribution to the literature.
  • With 5 years of follow-up, local recurrence and overall survival rates appear to be acceptable and equivalent to those documented for traditional, whole breast radiotherapy with boost after lumpectomy (Santiago RJ, IJROBP, 2006).
  • The importance of considerably longer follow-up should not be undervalued, however. Large studies have demonstrated that patients treated for early-stage breast cancer remain at risk for recurrent disease for at least 15 years after having completed treatment (Santiago RJ, IJROBP, 2006). This risk appears to be relatively constant.
  • Additionally, the authors do not comment on cosmetic outcome following treatment with Mammosite® RTS. Certainly, the use of implant-based radiotherapy raises questions regarding cosmetic outcome when compared to external beam radiotherapy, and these questions are largely unanswered. In addition, the delivery of an accelerated schedule of radiation to only a small part of the breast raises concern for breast asymmetry resulting years after treatment. Analysis of cosmetic outcome would be interesting at this point, and potentially more interesting with increased follow-up.
  • This study has relatively short follow-up compared to the breast literature as a whole; however, it represents one of the first large analyses of PBI delivered with the Mammosite® RTS. This system is employed to treat a large number of patients after lumpectomy with early stage breast cancer, and this trial is certainly an important contribution to their care. As follow-up time increases, future studies will offer long-term perspective on both cancer outcomes and cosmetic results for patients who choose this method of treatment.

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