Results and Discussion
Primary ectopic breast carcinoma is rare, accounting for 0.3 to 0.6% of all breast cancers.(4) It can arise anywhere along the bilateral embryological mammary streaks where accessory breast tissue persists, the most common location being the axilla (60-70%).(5) Due to its rarity and the paucity of published data, the management of ectopic axillary breast cancer is often conducted using the same principles as orthotopic breast cancer, in which the patient may be offered a mastectomy or standard breast conservation therapy approach consisting of wide local excision and SLN biopsy followed by radiation therapy. In 2005, the ACOSG Z0011 trial demonstrated that axillary lymph node dissection may be avoided in early-stage breast cancer patients with <3 positive SLNs.(3) To identify SLNs intraoperatively, radionuclide tracers such as Tc-99m and/or blue dye (e.g., methylene blue or isosulfan blue) are injected immediately prior to surgery. These principles have been routinely applied to the patient with an axillary primary tumor, even in the absence of definitive data supporting this approach.
A major challenge with the conduct of SLN biopsy in axillary breast cancer is the choice of site for tracer injection. Even in orthotopic breast cancer, the options of peritumoral, subareolar and periareolar injections are debated. In a prospective randomized clinical trial of four hundred breast cancer patients undergoing SLN mapping and biopsy, Povoski et al. demonstrated that intradermal injection of 99m-Tc into the skin overlying the breast cancer resulted in a significantly greater frequency of localization and decreased time to first localization by lymphoscintigraphy as compared to the intraparynchemal or subareolar injection.(6) However, few reports have described the use of lymphatic mapping with SLN biopsy for ectopic axillary breast cancer, and the injection technique is rarely described. In a review of the literature, just 16 reports of SLN biopsy for axillary breast cancer were identified within 14 manuscripts (Table1).(4, 7-19) Of these 16 patients, three (19%) underwent radionuclide tracing with lymphoscintigraphy only, three (19%) underwent tracing with blue dye only, six (37%) underwent dual tracing with radionuclide and dye, and the mapping technique in four (25%) patients were unreported. Injection site was reported in just six patients.
The use of radionuclide tracer or blue dye to identify SLNs in axillary breast cancer poses a potential challenge. The proximity of the axillary tumor to the regional lymph nodes may lead to a “shine-through” effect, by which it becomes difficult to identify an area of tracer localization in the axilla as a result of the lower gamma counts from the node(s) being obscured by the higher counts at the injection site. In a report by Uenaka et al ., Tc-99m and indigo carmine were injected into the ipsilateral areola pre-operatively. However, the axillary SLNs were unable to be identified by lymphoscintigraphy or hand-held gamma probe during surgery due to the shine-through effect, and no blue dye-filled tracts or nodes were seen.(15) In contrast, Patelet al. reported that SLN biopsy was successful in three patients when periareolar injection of Tc-99m was combined with peritumoral isosulfan blue injection.(8) In a patient who had previously undergone excisional biopsy of an ectopic axillary breast cancer, Alavifardet al. reported that pre-operative injections of Tc-99m into both ends of a surgical scar resulted in SLN uptake as measured via gamma probe.(10) Peritumoral injection of indigo carmine was reported by Lee et al., although it was not specified whether the dye was successfully taken up by the SLNs.(19)
In the present report, the tracer dose was divided into three equal portions and injected at three peritumoral sites. One portion was injected intradermally into the skin directly overlying the cancer and a second portion was injected into the primary tumor itself. A third portion was injected into the peri-tumoral subcutaneous tissues just posterior to the primary cancer. In this manner, it was theorized that multiple pathways were provided by which the tracer could enter the regional lymphatics and reach the SLNs. This approach permitted the successful identification of the SLNs intraoperatively with minimal shine-through and without the use of isosulfan blue dye. Of note, careful positioning of the gamma probe away from the injection site and toward the axillary region led to low levels of shine-through.