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.