European Journal of Nuclear Medicine and Molecular Imaging | 2021
Is it time to include [18F]FDG-PET/CT in the diagnostic work-up for lymph node staging in cN0 vulvar cancer patients?
Abstract
The study from Rufini et al. [1] published in this issue of the EJNMMI is the largest series of vulvar cancer patients preoperatively staged with [F]FDG-PET/CT. Given the scarcity of this disease and the importance of nodal staging, this study brings important insights to the nuclear medicine and oncology communities. Current guidelines for the management of vulvar squamous cell cancers describe a limited role for [F]FDG-PET/CT. The most recent published guidelines from the National Comprehensive Cancer Network (NCCN) [2] recommend only to consider of [F]FDG-PET/CT (including neck/chest/abdomen/pelvis/groin) at initial diagnosis for T2 or larger tumours or if metastasis is suspected. The European Society of Gynecologic Oncology (ESGO) Vulvar Cancer Guidelines full report from 2017 includes imaging of the groins with ultrasound (US), PET/CT orMRI prior to sentinel lymph node assessment as a Grade C recommendation [3]. According to the ESGO guidelines, sentinel node biopsy (SNB) is recommended in patients with unifocal cancers of less than 4 cm without suspicious groin nodes. If lymph node metastases are diagnosed pre-operatively, inguinofemoral lymphadenectomy should be performed and CT or PET/CT can rule out involvement of pelvic nodes to plan also pelvic nodal debulking. The 2020 American College of Radiology Appropriateness Criteria® for Staging and Follow-up of Vulvar Cancer rates [F]FDG-PET/CT as “usually appropriate” for initial staging for patients with a primary tumour greater than 4 cm or tumour of any size with more than minimal involvement of the urethra, vagina or anus [4]. In each of these, and other relevant national guidelines in which there is discussion of [F]FDGPET/CT, no studies as large as the cohort reported here by Rufini et al. are referenced. The recent systematic review and meta-analysis by Triumbari et al. included only 10 smallvolume studies [5]. Thus, it is likely that the study by Rufini et al. will shape future expert recommendations for management of vulvar cancer in both pre-operative assessment of the groin and pelvis, and for use in treatment planning for patients planned for definitive radiotherapy. The study from Rufini et al. is a single institution retrospective study involving 160 patients with vulvar cancer (VC) treated within a multidisciplinary standardized approach. PET examinations were acquired on two systems, one of them equipped with point-spread-function (PSF) modelling, which not only improves detectability of small cancer deposits [6] but also leads to a significant increase in SUV metrics compared to conventional algorithms and therefore requires harmonization [7]. In this study, harmonization was achieved by using a post filtering step, though eventually visual analyses overcome SUV-based analysis. Rufini et al. fully covered the information assessable on PET/CT images, namely visual and quantitative (SUVbased) interpretation of PET images as well as CT criteria, i.e. short axis of pelvic nodes. Interestingly, visual analysis overcame SUV-based criteria. Overall, sensitivity (Se) and negative predictive value (NPV) in discriminating metastatic from non-metastatic nodes were 85.6% (95% CI 78.3–92.8) and 91.2% (95% CI 86.7–95.8%), respectively. The authors also concluded that CT criteria were not useful on top of PET interpretation, as the aim of improved interpretation criteria was to reduce the risk of overlooked LN metastases, and PET+CT criteria in fact slightly altered Se and NPV. Hence, simple visual assessment can be safely used for interpretation in busy PET centres. This article is part of the Topical Collection on Oncology –Genitourinary