Mitotic count of fine needle aspiration material of gastrointestinal stromal tumours of the stomach underestimates actual mitotic count

Abstract

Introduction A mitotic count is required for histological grading in resections of gastrointestinal stromal tumours (GISTs). However, no consensus on the utility of mitotic count in fine needle aspiration (FNA) GIST material currently exists. This study examines the relationship between mitotic counts of FNAs and subsequent resections of GISTs of the stomach. Materials and methods We identified 39 cases of GISTs of the stomach diagnosed via FNA at our institution between January 1, 2014, and December 31, 2019, with subsequent resection. We noted if rapid on‐site evaluation (ROSE) was performed. Cell block (CB) material from FNAs was analysed for total area, percentage containing neoplastic cells, and number of mitoses. We compared the mitotic counts in CBs and subsequent resections with t tests. Results ROSE was performed in 82% of cases and called adequate every time. Mean values for total CB area, neoplastic material percentage, and area of neoplastic cells were 54.7 mm2 (range 1‐986), 45% (range 10%‐90%), and 19.2 mm2, respectively; 27 cases (69%) had greater than 50 high powered fields of GIST material in the CB. Mean numbers of mitoses per 5 mm2 were 0.38 (range 0‐11) for CBs versus 5.92 (range 0‐70) for resections (P < 0.05). Conclusion At our institution, ROSE adequacy of spindle cell lesions focuses on diagnosing GIST rather than obtaining adequate material for histological grading. Mitotic figures were statistically lower in FNA CB material than subsequent resections, and using mitotic counts from CB material may underestimate the histological grade of GISTs of the stomach.

Reliability of assessing morphologic features with prognostic significance in cytology specimens of epithelioid diffuse pleural mesothelioma and implications for cytopathology reporting

“…The 2021 WHO classification also recommends the reporting of nuclear grade in pathology reports of E‐DPM 10,12,23 . A limitation of applying this grading system to cytology specimens is that mitotic counts in cytology specimens are known to be unreliable 53 . In the current study, we found it difficult to assess mitoses in cytology specimens because mitoses were generally not preserved in aspirate smear slides, and in some cases low tumor cellularity limited our ability to provide accurate mitotic counts.…”

“…10,12,23 A limitation of applying this grading system to cytology specimens is that mitotic counts in cytology specimens are known to be unreliable. 53 In the current study, we found it difficult to assess mitoses in cytology specimens because mitoses were generally not preserved in aspirate smear slides, and in some cases low tumor cellularity limited our ability to provide accurate mitotic counts. For these reasons, mitotic count was not evaluated in the present study, and therefore it was not possible to perform formal 2021 WHO grading of E-DPM in cytology specimens.…”

“…The following morphologic features were documented for paired cytology and surgical pathology samples with previously established criteria: (1) the presence of architectural patterns including tubulopapillary, trabecular, micropapillary, and solid 13 ; (2) the presence or absence of pleomorphic cytologic features 13,14 ; (3) the presence or absence of tumor necrosis 9 ; and (4) a nuclear atypia score of 1–3 18 . Even though mitotic count is included in the current WHO grading system for E‐DPM, 23 mitotic counts were not performed in this study given the unreliability of mitotic counts in cytology specimens 53 …”

“…18 Even though mitotic count is included in the current WHO grading system for E-DPM, 23 mitotic counts were not performed in this study given the unreliability of mitotic counts in cytology specimens. 53 Diagnostic criteria for assessment of architectural patterns in this study were initially described by Kadota et al 13 Briefly, a tubulopapillary pattern shows tubular and/or papillary structures.…”

Ki‐67 index assessment on FNA specimens of gastrointestinal stromal tumor: Correlation with mitotic rate and potential predictive value for risk stratification

“…Although it is challenging to count mitosis in limited cytology materials, 22 alternative methods such as Ki-67 index have been explored but are extremely limited in the literature. 12,23,24 Thus, our current study aimed to (1) assess the correlation between Ki-67 index in EUS-FNA cytology blocks and mitotic count in follow-up surgical specimens, and (2) evaluate whether Ki-67 index can be used to predict mitotic rate and risk assessment preoperatively.…”