[99mTc]Tilmanocept Lymphscintigraphy after inconclusive [99mTc]Nanocolloid Scan in Breast Cancer.

Lymphatic mapping for identification and subsequent removal of the sentinel lymph node (SLN) is an established procedure in breast cancer and cutaneous melanoma to minimize the extent of surgery (and thus, associated morbidity), simplify histopathological processing and subsequently provide prognostic information and help choose the optimal patient management. Established methods for SLN mapping include visual identification of nodal staining after peritumoral injection of a (blue) dye or the use of lymphoscintigraphy with technetium-labelled nanocolloid. In experienced hands, success rates for both methods exceed 95 %, nonetheless in some patients they fail despite correct application and imaging techniques. Potential reasons for false-negative SLN detection rates -beyond poor tracer injection technique or imaging of the wrong nodal basin- include inadequate pathologic examination of the SLN or complete replacement of the SLN with neoplastic disease, causing the injected tracer to completely bypass the infiltrated node 1.Beyond colloid particles, the more specific receptor-targeting small molecule [^99mTc]Tilmanocept has recently been approved for scintigraphic SLN detection. Tilmanocept, or mannosyl diethylene-triamine-pentaacetate (DTPA) dextran, has a small molecular size of approximately 7 nm and works via specific binding to the mannose receptor (CD206) 2. The mannose receptor is particularly overexpressed on macrophages and dendritic precursor cells within lymph nodes, thus uptake in lymph nodes is not dependent on particle size 2, 3. In pilot studies scintigraphic SLN detection with [^99mTc]Tilmanocept was superior to dye staining 4. Given its beneficial properties, [^99mTc]Tilmanocept might offer advantages over the alternatively used radiocolloids. We present four cases of [^99mTc]Tilmanocept application after inconclusive or unsuccessful attempts of SLN detection using [^99mTc]nanocolloid lymphoscintigraphy.