Siavash Jabbari, MD
When it comes to breast-conserving surgery, the definition of an adequate margin has always been a controversial subject. Many women with negative margins undergo re-excisions after the initial lumpectomy to obtain a wider clear margin due to the belief that a wider margin further reduces the likelihood of recurrence.
Earlier this year, the Society of Surgical Oncology (SSO) and the American Society for Radiation Therapy (ASTRO) released new surgical guidelines to create a clear and comprehensive approach for physicians. Following a comprehensive review of the available literature, the multidisciplinary panel concluded there is no additional benefit to the removal of larger amounts of healthy tissue beyond “no ink on tumor”. Experts hope the guidelines will reduce unnecessary re-excisions and give eligible patients the confidence to pursue breast-conserving surgery.
Radiation oncologist Siavash Jabbari, MD, of Sharp Healthcare, San Diego, Calif., discusses the significance of the new guidelines, how they’ve influenced his practice, and his thoughts on ideal margins for delivering breast brachytherapy.
In the margin guidelines released earlier this year, what were the most significant conclusions reached by the consensus panel?
The SSO-ASTRO, and as endorsed by ASCO, conclude that “no ink on tumor” (either invasive or in situ component) is a sufficient negative margin status for stage I-II breast cancer patients treated with breast conservation surgery and whole breast irradiation. While a positive margin(s) significantly increases recurrence rates, routine further normal tissue resection and/or wider negative margins than “no ink on tumor” is not supported by the current evidence and in the above setting. Factors such as whole breast fractionation, boost dose, lobular histology, biological subtype, young age, extensive intra-ductal component, and choice of systemic therapy should not as a rule alter the above recommendations. In general, it’s expected that the appropriate adoption of these guidelines will decrease inappropriate re-excision rates for patients.
Prior to the guidelines, what did you consider to be an adequate margin for breast-conserving therapy?
Our institution has always taken a holistic multi-disciplinary approach to margin status adequacy post-breast excision and further recommendations. Prior to the publication of the above guidelines, however, we generally employed a lower threshold for recommending re-excision in the setting of “close” margins of less than 1-2mm.
Have the guidelines changed the way you practice?
We generally adhere to the above guidelines’ definition of a negative margin in the appropriate clinical setting. As discussed in the ASCO endorsement of these guidelines, however, discretion is used in unusual clinical circumstances as indicated, and with multi-disciplinary input (for example, focal deep positive margin in the setting of full resection to and including the pectoralis fascia is not considered a true positive margin). The standard of post-lumpectomy mammography to rule out residual suspicious calcifications is also adhered to in our practice prior to confirming the adequacy of resection.
The guidelines are specifically for breast-conserving surgery with whole breast irradiation – what do you consider to be an adequate margin for BCS with brachytherapy?
While there isn’t necessarily conclusive data suggesting that patients treated with brachytherapy need different margins, our institution considers a resection margin of 2mm or greater to be ideal for partial breast irradiation, which is concordant with existing guidelines. Tumor margins of less than 2mm are evaluated individually by the multidisciplinary team and in full discussion with the patient, considering the number and severity of other potential adverse features and patient age.
One of the advantages of multi-lumen brachytherapy techniques, such as with the SAVI applicator, is that we have been able to asymmetrically shape the therapeutic dose cloud by differentially loading the lumens to better accommodate such “focally close margins.” This enables us to treat a larger volume of tissue deemed at risk for higher microscopic disease burden in the direction of the close margin (i.e., 1.5-1.7cm PTV expansion vs. 1cm). Multi-lumen brachytherapy allows for this dosimetric advantage in terms of an oncologically shaped and tumor-targeted dose distribution, while maintaining acceptable coverage and adjacent normal structure dose (opposing skin or chest wall).
Moreover, brachytherapy is unique in that it has a built-in tumor bed boost. The typical prescription dose for brachytherapy (34Gy at the PTV expansion) is the calculated biological equivalent to whole breast irradiation. Thus, everything within the PTV expansion is receiving a larger dose than the prescription dose. Although requiring validation, it is hypothesized that this dose heterogeneity created in the portion of the PTV that is asymmetrically expanded would likely correspond to the tissue at highest risk of microscopic tumor burden (close margin), and may provide an additional oncological therapeutic benefit.
Dr. Jabbari is a radiation oncologist at Sharp Healthcare in San Diego, Calif. He focuses on incorporating new technology and techniques to improve patient outcomes and minimize side effects of cancer care.