Prognostic significance of morphological growth patterns and mitotic index of epithelioid malignant peritoneal mesothelioma

Our plain-English summary of Prognostic significance of morphological growth patterns and mitotic index of epithelioid malignant peritoneal mesothelioma, by A.M. Krasinskas, A.C. Borczuk, D.J. Hartman, et al (Histopathology, 2016).

The study

• Authors: A.M. Krasinskas, A.C. Borczuk, D.J. Hartman, J.A. Chabot, R.N. Taub, A. Mogal, J. Pingpank, D. Bartlett, S. Dacic
• Journal: Histopathology
• Published: 2016;68(5):729-37
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Aims: The prognostic significance of histological subtyping of epithelioid pleural mesotheliomas has been recently reported, but similar data are lacking for peritoneal mesotheliomas. The aim of this study was to investigate possible relationships between histological growth patterns of epithelioid peritoneal mesotheliomas, clinicopathological features, and patient outcome.

Methods And Results: Eighty-four cases of chemotherapy-naive epithelioid peritoneal mesothelioma were classified into tubulopapillary, micropapillary, papillary, tubular, solid and trabecular growth patterns. Pathological features such as depth of invasion, lymphocytic host response, mitotic count, nuclear grade, lymphovascular invasion, lymph node metastasis and stromal desmoplasia were analysed. The most common histological patterns were solid (n = 37, 44%), tubulopapillary (n = 24, 29%), and micropapillary (n = 11, 13%). The overall median survival was 36 months. Patients with solid mesothelioma had shorter overall survival (median, 29 months) than patients with tubulopapillary and micropapillary growth patterns (median, 51 and 53 months, respectively; P = 0.053). A high mitotic index (>5 in 50 high-power fields) was found to be associated with poor survival (P < 0.03). A moderate to severe lymphocytic host response was associated with longer median survival (P = 0.13).

Conclusions: Our study highlights the prognostic importance of the solid growth pattern among diffuse epithelioid peritoneal mesotheliomas, and reaffirms mitotic index as a predictor of overall survival.

© 2015 John Wiley & Sons Ltd.

In plain English

This study examined tumour tissue from 84 patients with the epithelioid type of malignant peritoneal mesothelioma (mesothelioma of the abdominal lining), drawn from the archives of the University of Pittsburgh Medical Center and Columbia University Medical Center. All had cytoreductive surgery and no prior chemotherapy. Most also received heated chemotherapy inside the abdomen (HIPEC). Four pathologists classified each tumour by its main growth pattern and other microscopic features, then compared these with survival. The article does not address asbestos exposure. The most common patterns were solid (37 patients), tubulopapillary (24) and micropapillary (11). Median overall survival for all patients was 36 months. Median survival was 29 months for solid tumours, compared with 51 months for tubulopapillary and micropapillary combined. This difference approached but did not reach statistical significance (P = 0.053). Tumours with a high mitotic index (more than 5 dividing cells per 50 high-power fields) had median survival of 23 months, compared with 51 months for a low index (P = 0.027). The authors concluded that the solid pattern was associated with poorer prognosis and confirmed the importance of mitotic index.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Pathology study of archived tumour samples (retrospective case series) with survival analysis
• Who was studied: 84 patients with epithelioid malignant peritoneal mesothelioma who had cytoreductive surgery (most with HIPEC) and no prior chemotherapy, from the University of Pittsburgh Medical Center and Columbia University Medical Center, New York; 59 men and 25 women; median age at surgery 64 years. Study years are not stated.
• Exposure: Asbestos or other exposures were not studied. The factors examined were tumour growth patterns and microscopic features such as mitotic count, nuclear grade, depth of invasion, lymphocytic host response, lymphovascular invasion, lymph node metastasis and stromal desmoplasia.
• Main results:
  • Predominant growth patterns among the 84 tumours were solid (n = 37, 44%), tubulopapillary (n = 24, 29%) and micropapillary (n = 11, 13%). The remaining patterns were tubular (6), papillary (4) and trabecular (2).
  • Median overall survival for all patients was 36 months.
  • There was no difference in overall survival when all six growth-pattern groups were compared.
  • After the small tubular, papillary and trabecular groups were removed from the analysis, median overall survival was 51 months in the tubulopapillary group, 53 months in the micropapillary group and 29 months in the solid group.
  • Tubulopapillary and micropapillary combined had a median survival of 51 months, compared with 29 months for solid tumours. The authors described this difference as approaching statistical significance (P = 0.053).
  • Median survival was 51 months for cases with a low mitotic index (5 or fewer per 50 high-power fields) and 23 months for cases with a high mitotic index (more than 5 per 50 high-power fields) (P = 0.027).
  • Median survival was 53 months for cases with a moderate to marked lymphocytic host response and 29 months for cases with none to mild. This difference was not statistically significant (P = 0.13).
  • High nuclear grade was found in 29 of 35 solid-pattern cases (83%). Nuclear grade was more evenly split in the other patterns (P = 0.043).
  • Among the 16 cases with lymph nodes available, lymph node metastases were found in 5 of 9 solid-pattern cases (55%) and 2 of 7 non-solid cases (29%). This difference was not statistically significant (P = 0.073).
• The authors' conclusion: The authors concluded that the solid growth pattern was associated with aggressive behaviour and poorer prognosis compared with tubulopapillary and micropapillary patterns. They also concluded that the study validated the importance of mitotic index, while other features such as nuclear grade, depth of invasion and stromal desmoplasia were not strong predictors of outcome.
• Limitations the authors state:
  • Most patients had cytoreductive surgery with HIPEC. Some features, such as nuclear grade, might predict survival in untreated or differently treated patients even though they did not in this group.
  • The tubular, papillary and trabecular groups were too small to include in the survival comparisons.
  • Only a small number of cases had lymph nodes available for evaluation.
  • The pleomorphic pattern was never the dominant pattern, so the authors could not judge its significance in peritoneal mesothelioma.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma, Peritoneal mesothelioma.

Medical terms in this study, explained in our Lexicon: Mitotic Index, Epithelioid, Peritoneal Mesothelioma, Pleural Mesothelioma, Chemotherapy, Tubulopapillary, Micropapillary, Trabecular.

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• High Wilms' tumour gene (WT1) expression and low mitotic count are independent predictors of survival in diffuse peritoneal mesothelioma — A. Scattone, G. Serio, et al. (2012)
• Prognostic significance of Ki67 expression in malignant peritoneal mesothelioma — K. Pillai, M.H. Pourgholami, et al. (2015)

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