SAN ANTONIO – Positive margin and reoperation rates were similar for radio-guided seed localization and wire-guided localization of nonpalpable breast tumors in a prospective multicenter trial – in contrast to results from previous studies.

In an intent-to-treat analysis of 305 women with confirmed invasive or ductal carcinoma in situ who were undergoing localization and breast-conserving surgery, positive margin rates were 10.5% for radio-guided seed localization (RSL) and 11.9% for wire-guided localization (P = .990).

Rates of positive plus close margins (defined as disease within less than 1 mm) were 19% for the seed group and 22% for the wire group (P = .609), Dr. Peter Lovrics reported at a symposium sponsored by the Society of Surgical Oncology.

Rates of reoperation – either re-excision of margins or mastectomy – were also similar (19% and 15%, respectively) in the wire and seed groups, said Dr. Lovrics of the department of surgery at McMaster University in Hamilton, Ont.

The feasibility of RSL for identifying occult breast tumors was first reported a little more than a decade ago, and RSL has been rapidly adopted in many European countries. The procedure involves intratumoral injection of a radiotracer to identify the primary tumor and sentinel lymph nodes for intraoperative gamma probe–guided dissection.

In a recent literature review of 12 studies, Dr. Lovrics and his associates found that RSL yields lower positive margins (odds ratio, 0.367) and fewer reoperations (OR, 0.347) than does wire-guided localization, and three of those studies also suggested improved cosmesis (Eur. J. Surg. Oncol. 2011 Feb. 16 [E-pub ahead of print]).

When asked why RSL failed to produce significantly better outcomes, Dr. Lovrics said it may be that with a larger sample size, RSL would be potentially better, yielding results similar to those of other studies. Notably, overall positive margin rates were low for both groups and were much higher for wire-guided localization in most other studies.

"This may be partially attributed to the fact that all patients had a preoperative core biopsy and a confirmed diagnosis of cancer, so all of the procedures were definitive operations," he said in an interview. "In some other studies, not all patients had confirmed cancer and some operations were diagnostic in intent. Otherwise, the study population was typical – similar to other studies in tumor characteristics."

In the current study, there were 152 patients in the seed group and 153 in the wire group, with 6 patients crossing over to the wire group because the seed did not arrive at the hospital on the day of surgery. Mammogram findings included a mass in 47% of the wire group and in 50% of the seed group, and microcalcifications in 11% and 14%, respectively. Three-fourths of patients had a mass present on ultrasonography. Their average age was 60 years.

Secondary outcomes between groups were very similar, except for a significantly shorter operative time of 19 minutes with seed localization vs. 22 minutes in the wire group (P less than .001), Dr. Lovrics said. Excision difficulty was also ranked significantly easier for surgeons with seed localization (P = .008).

Factors such as skin removal and whether the dissection was taken to the chest wall were similar, as were the number of additional cavity margins excised and postoperative complications at 1 month, he said during a breast-focused plenary session.

Pain-reported anxiety during localization was similar in both groups, although patients in the seed group reported significantly less pain during the localization procedure than did those in the wire group (P = 0.38). An analysis of cosmetic results is ongoing.

Dr. Lovrics said that RSL allows exquisite and precise localization of the tumor, and that radiation exposure to patients and health care workers is negligible.

"For the surgeon, it provides very real-time, enhanced guidance for localization and is preferred by surgeons," he concluded. "Radio-seed localization is an acceptable alternative to wire-guided localization."

During a discussion of the study, audience members asked whether a cost analysis had been performed and whether the seeds were placed on the day of the surgery. Dr. Lovrics said the seeds and the wire both cost about $50, and that they currently place the seed on the day of surgery, but they hope to insert it earlier to further reduce OR time.

When asked whether a radiograph is still needed after seed localization, Dr. Lovrics said that a postoperative radiograph is still essential because of the risk of seed migration. Seeds were misplaced in four cases, one seed migrated, one wire migrated, and one wire fell out.

The Canadian Breast Cancer Foundation funded the study. Dr. Lovrics and his coauthors reported no conflicts of interest.

Techniques Compared for Breast Tumor Detection