Radiation Therapy for Early-Stage Breast Cancer
Six randomized trials, both in the United States and Europe, demonstrated conclusively that lumpectomy followed by radiation therapy to the conserved breast tissue was as effective as modified radical mastectomy in controlling breast cancer and in achieving commensurate survival. The ideal candidate for breast-conservation therapy is a patient who has a unifocal tumor 5 cms or smaller in size that is excised with a negative margin.
Although the definition of a negative margin is somewhat open to interpretation, several institutional retrospective reviews have indicated that a margin of 2 mm or greater, plus postoperative radiation, is sufficient to achieve control within the breast at a rate of approximately 93-95%.
Ordinarily, when surgery is performed to remove a breast malignancy, a 1cm gross margin of normal tissue is considered desirable. In fact, tumors are often seen to extend beyond the initial anticipated size of the tumor. The analysis of mastectomy specimens performed by Roland Holland has revealed that subclinical foci of cancer frequently exist up to 4 cms from the periphery of the tumor.
Therefore, the value of removing a 1-2 cm rim of normal tissue along with the primary tumor is to eliminate a significant burden of subclinical disease. Given the limits of pathologic sampling, it stands to reason that a patient who undergoes lumpectomy with a resultant positive margin will have a commensurate large residual tumor burden that will decrease the patient’s likelihood of local control with moderate doses of radiation.
The desire to achieve tumor excision with a negative margin will commonly require the patient to return to the operating room for a second excision of the tumor bed. Occasionally, the cosmetic outcome is degraded by further surgery, highlighting the importance of collaboration between the radiologist, pathologist and surgeon to achieve excellent localization, tissue excision and margin analysis at the initial surgery.
A further element in the selection of ideal candidates for breast-conservation therapy is the ability to follow the patient mammographically. Those patients who have tumors detected mammographically, particularly by virtue of microcalcifications, must undergo postexcision mammography to assess the status of the breast tissue in the region of excision.
Specimen radiography simply does not substitute for postexcision mammography with magnification views of the operated site in providing the level of security that all abnormal findings have, indeed, been removed. This study should be performed prior to embarking upon a course of postoperative radiation. Patients who have multicentric breast cancer, particularly in different quadrants of the breast, are poor candidates for breast-conservation therapy as local control in these patients is demonstrably lower.