The value of lymph node ultrasound and whole body PET/CT in stage IIB/C patients prior to SLNB

e22079 Background: Stage IIB/IIC (pT3b-T4N0) patients are known to have high-risk primary tumors, even higher risk than some stage IIIA/B melanomas (AJCC Staging System 8th edition), however they follow the same routine to sentinel lymph node biopsy (SLNB) as more low-risk tumors. A priori the risk of finding SLNB or other metastases is much higher for these thick and/or ulcerated primary melanomas compared to the thinner ones. Guidelines are not conclusive regarding the use of preoperative imaging in these cases. Recently, a trend to more frequently use cross-sectional imaging has been noticed. However, others have previously shown that preoperative ultrasound was the most sensitive. The aim of this pilot study was to assess the value of ultrasound (US) and Positron Emission Tomography/Computerized Tomography (PET/CT) prior to SLNB for stage IIB/C (pT3b-T4N0) melanoma patients. Methods: Starting 2019-04, all patients with a pT3b melanoma or higher (8th AJCC) were included. All patients underwent US and PET/CT before their planned lymphoscintigraphy and routine SLNB. Suspected metastases were confirmed with cytologic puncture. Results: A total of 20 patients were screened. Seven patients (35%) had metastases detected by imaging: one by PET/CT, three by US and three by both imaging modalities. Three of these metastases were detected by US as well as PET/CT. All metastases were nodal. For all seven patients treatment was altered to lymph node dissection with adjuvant therapy. Of the 13 patients in whom no metastases were identified by imaging, six (46%) still had a positive sentinel node (SN). Conclusions: This study showed that this select group of patients had a high risk of metastases prior to SLNB and that all recurrences except one, were detected by ultrasound. This suggests that nodal staging with US is sufficient and can replace the need for SLNB when metastases is proven with cytology. Despite negative imaging, SLNB cannot be foregone for pT3b-pT4N0 melanoma patients, as many still have an involved SN. Cross-sectional imaging can be reserved for patients after positive cytology or SN to confirm the absence of distant visceral metastases.