Sentinel lymph node tumour burden using digital cell count estimation predicts outcomes in melanoma

Abstract

Background and aims Cutaneous melanoma often metastasises in primis to sentinel lymph nodes (SLNs). Currently, there is no standardized method of characterizing the micrometastatic tumour burden in SLN biopsies for melanoma. Different criteria have been developed to evaluate SLN biopsies, yet none consider the number of cells identified. Here, we used software analysis to digitally quantify metastatic tumour burden within SLNs and correlated these data with clinicopathological and prognostic information. Methods and results We identified 246 cases of SLN biopsies, including 63 positive (26%) and183 (74%) negative for metastatic melanoma. Digital cell counting was performed within the greatest metastatic focus and the entire metastatic tumour burden within the same SLN. Increasing cell count in the largest metastatic deposit correlated with the previously described Rotterdam [Spearman's r = 0.91; 95% confidence interval (CI) = 0.84, 0.94], Starz (Spearman's r = 0.78; 95% CI = 0.68, 0.87) and Dewar criteria (P < 0.01), validating our method of using cell count to define SLN tumour burden. Additionally, increasing cell count was associated with decreased metastasis‐free survival (hazard ratio = 2.29; 95% CI = 1.22, 4.31). Conclusion These data support the use of computerized cell count analysis for prognostication of outcomes in patients undergoing SLN biopsy.

Sentinel lymph node assessment in melanoma: current state and future directions

“…17,24,25 C E L L C O U N T Stratification of tumour burden by cell count was first utilised by Carlson et al, 34 categorising submicrometastases into two groups: clusters of cells (10-30 grouped cells) and isolated cells (one to > 20 individual cells). Since the introduction of this categorisation, several additional studies have also investigated the association of the number of cells present in a metastatic deposit and prognosis 18,35,36 Increased cell count is generally associated with decreased relapsefree survival, with one study citing a cut-off of > 30 cells. 18,35 Although metastatic deposits with few cells present are correlated with a better prognosis, a small number of patients undergoing surveillance-only protocols still experience disease recurrence, highlighting a need to further investigate the association of this parameter with measures of prognosis.…”

“…Since the introduction of this categorisation, several additional studies have also investigated the association of the number of cells present in a metastatic deposit and prognosis 18,35,36 Increased cell count is generally associated with decreased relapsefree survival, with one study citing a cut-off of > 30 cells. 18,35 Although metastatic deposits with few cells present are correlated with a better prognosis, a small number of patients undergoing surveillance-only protocols still experience disease recurrence, highlighting a need to further investigate the association of this parameter with measures of prognosis. 36 Additionally, a theoretical advantage of this method is that it prevents overestimation of tumour burden in cases where numerous individual tumour cells comprise metastasis, as opposed to groups of tumour cells.…”

“…However, new and emerging technologies of digital pathology on highresolution scanned images and analytical software may help in obtaining an accurate cell counts which will facilitate further studies into the association of cell count with prognosis. 18 These measures of cell count are well correlated with the Rotterdam, Starz and Dewar criteria 18 New considerations in evaluating tumour burden…”

“…31 The process of automating measurements generally involves digitisation of the histological slides into high-resolution images using a digital slide scanner. 18,31 After the creation of this repository of images, an image-analysing software can be programmed to quantify metastatic burden. 18,31 Another recent advancement has been the development of light sheet fluorescence microscopy (LSFM), which has recently been utilised in conjunction with an algorithm enabling the display of LSFM data to quantify total metastatic deposit volume.…”

“…18,31 After the creation of this repository of images, an image-analysing software can be programmed to quantify metastatic burden. 18,31 Another recent advancement has been the development of light sheet fluorescence microscopy (LSFM), which has recently been utilised in conjunction with an algorithm enabling the display of LSFM data to quantify total metastatic deposit volume. 86 There is good agreement between automated digital estimates of tumour burden volume and manual estimates of the same parameter, with similar hazard ratios.…”