To boost or not to boost: decreasing radiation therapy in conservative breast cancer treatment when "inked" tumor resection margins are pathologically free of cancer.

A retrospective study was performed to compare local treatment approaches for 108 treated breasts in 105 patients with Stage I or II breast cancer. Six cases with intraductal carcinoma have shown no evidence of recurrence. The other 102 cases had invasive cancer. In 54 treated breasts in 53 patients, the treatment approach involved surgical resection of the primary tumor, pathological determination of tumor-free "inked" specimen margins and 5000 cGy to the whole breast. Local radiation therapy (RT) boosts to the primary site were not given. This approach produced a 100% local control rate (mean follow-up of 38 months). In 28 treated breasts in 27 patients, the treatment approach involved tumor excision without evaluation of specimen margins followed by RT which included a local boost by either interstitial Iridium-192 implant or electron beam. This approach yielded an actuarial local control rate of 87% at 48 months (mean follow-up of 47 months). The difference in local control rate between the two groups was statistically significant (p less than 0.03). Among patients with clear surgical margins who received a local RT boost, 1 of 9 developed a local recurrence. Among those with tumor involving specimen margins who received a local boost, 1 of 8 developed local recurrence. Local recurrence developed more frequently among patients with poorly differentiated cancers (2 of 11 cases) than among those with other invasive cancers (3 of 91 cases). Comparison of treatment approaches was limited since poorly differentiated cancer was present in 25% of cases with unknown specimen margins, as compared with only 2% of those with clear surgical margins who did not receive a local RT boost. Our preliminary findings suggest that when "inked" primary tumor resection margins are pathologically free of cancer, 5000 cGy whole breast RT appears to be highly effective for local tumor control in patients with Stage I or II disease. Our results are inconclusive as to whether patients with poorly differentiated cancers should receive a local RT boost even when surgical margins are clear.