Lymphoseek: a molecular imaging agent for melanoma sentinel lymph node mapping

Anatomical and molecular imaging of skin cancer

Skin cancer is the most common form of cancer types. It is generally divided into two categories: melanoma (∼ 5%) and nonmelanoma (∼ 95%), which can be further categorized into basal cell carcinoma, squamous cell carcinoma, and some rare skin cancer types. Biopsy is still the gold standard for skin cancer evaluation in the clinic. Various anatomical imaging techniques have been used to evaluate different types of skin cancer lesions, including laser scanning confocal microscopy, optical coherence tomography, high-frequency ultrasound, terahertz pulsed imaging, magnetic resonance imaging, and some other recently developed techniques such as photoacoustic microscopy. However, anatomical imaging alone may not be sufficient in guiding skin cancer diagnosis and therapy. Over the last decade, various molecular imaging techniques (in particular single photon emission computed tomography and positron emission tomography) have been investigated for skin cancer imaging. The pathways or molecular targets that have been studied include glucose metabolism, integrin α_vβ₃, melanocortin-1 receptor, high molecular weight melanoma-associated antigen, and several other molecular markers. Preclinical molecular imaging is thriving all over the world, while clinical molecular imaging has not lived up to the expectations because of slow bench-to-bedside translation. It is likely that this situation will change in the near future and molecular imaging will truly play an important role in personalized medicine of melanoma patients.

Technical limitations of lymph node mapping in pancreatic cancer

AIM

The high incidence of lymphatic and peri-neural invasion in pancreatic cancer results in poor loco-regional control. Radical pancreatico-duodenectomy may achieve better loco-regional control, but is accompanied by increasing morbidity. Our hypothesis was that if intra-operative mapping of pathological lymph nodes (LN) is technically feasible in pancreatic cancer, it would allow for selective radical resection.

METHODS

In an ethically approved and statistically powered feasibility study of 72 (stopped after 20% enrollment) patients with suspected pancreatic cancer undergoing resection, we injected methylene blue dye peri- and intra-tumorally and studied its progress to identify putative 'sentinel lymph node(s)'. The Kausch-Whipple procedure (or total pancreatectomy, if required) was carried out in addition to radical LN dissection, which was evaluated histopathologically according to the Japanese criteria.

RESULTS

Over 18 months, 14/16 patients prospectively recruited underwent lymph node mapping and a mean of 20 (range 11-37) LNs per patient were harvested. Methylene blue dye injection identified blue LN(s) in 4/14 patients, none of which were positive for malignant deposits, whilst 10/14 patients had LN metastases. The commonest stations for LN metastasis were 17A or B (9/10), 8A (2/10) and 6 (3/10). The median survival for the 13 patients with cancer was 22.3 months (IQR: 10.4-30 months).

CONCLUSION

Sentinel lymph node mapping is not technically feasible in pancreatic cancer.

Sentinel lymph node mapping of breast cancer via intradermal administration of Lymphoseek

Lymphoseek is a molecular imaging agent specifically designed for sentinel lymph node (SLN) mapping. We conducted a Phase I trial which measured the injection site clearance and SLN accumulation after a single intra dermal injection of Lymphoseek or [99mTc]sulfur colloid protocol. Ten patients with breast cancer participated in this study. Five patients received an intradermal administration of 1.0 nmol of 99mTc-labeled Lymphoseek and five patients received an intradermal administration of filtered [99mTc]sulfur colloid (fTcSC). Lymphoseek exhibited a significantly (P<.001) faster injection site clearance than fTcSC. The mean Lymphoseek clearance half-time was 2.61+/-0.72 h compared to 24.1+/-17.7 h for fTcSC. The mean SLN uptake of Lymphoseek (1.1+/-.5%) and fTcSC (2.5+/-4.9%) was statistically equivalent (P=.28). When an intra dermal injection was employed, Lymphoseek demonstrated faster injection site clearance than fTcSC.