Incidence, Survival Analysis and Future Perspective of Primary Peritoneal Mesothelioma (PPM): A Population-Based Study from SEER Database

Our plain-English summary of Incidence, Survival Analysis and Future Perspective of Primary Peritoneal Mesothelioma (PPM): A Population-Based Study from SEER Database, by A. Ullah, A. Waheed, J. Khan, et al (Cancers, 2022).

The study

• Authors: A. Ullah, A. Waheed, J. Khan, A. Mishra, B. Tareen, N. Nama, N.R. Karki, M.S. Panezai, L.V. Zarate, J. White, F.D. Cason, N. Matolo, S. Misra, N.A. Karim
• Journal: Cancers
• Published: 2022;14(4)
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Primary peritoneal mesothelioma (PPM) is a rare and aggressive tumor arising from the visceral and parietal peritoneum. The diagnosis and treatment of PPM are often delayed because of non-specific clinical presentation, and the prognosis is worse. The current study investigated the demographic, clinical, and pathological factors affecting patient prognosis and survival in PPM.

Methods: Demographic and clinical data of 1998 patients with PPM were extracted from the Surveillance Epidemiology and End Results (SEER) database (1975-2016). The chi-square test, paired t-test, and multivariate analysis were used to analyze the data.

Results: The majority of PPM patients were male (56.2%, p < 0.005) and Caucasian (90.4%, p < 0.005, with a mean age of diagnosis was 69 ± 13 years. The grading, histological, and tumor size information were classified as "Unknown" in most of the cases, but when available, poorly differentiated tumors (8.7%), malignant mesothelioma, not otherwise specified (63.4%) and tumors > 4 cm in size (8%), respectively, were most common, p < 0.005. Chemotherapy was administered to 50.6% of patients, followed by resection (29.2%) and radiation (1.5%), p < 0.001. The cohort of PPM had a five-year overall survival of 20.3% (±1.1), compared to 43.5% (±5.9), 25.9% (± 8.4), and 18.7% (±1.6) for those with surgery, radiation, or chemotherapy alone, respectively. Poor differentiation (OR = 4.2, CI = 3.3-4.9), tumor size > 4 cm (OR = 3.9, CI = 3.2-4.5), Caucasian race (OR = 2.9, CI = 2.6-4.4), and distant SEER stage (OR = 2.5, CI = 1.1-3.2) were all linked with increased mortality (p < 0.001).

Conclusion: An extremely rare and aggressive peritoneal tumor, PPM may be difficult to identify at the time of diagnosis. Radiation therapy likely to have a limited function in the treatment of this condition, with surgery and chemotherapy being the primary choices. All PPM patients should be enrolled in a nationwide registry to improve our understanding of the pathogenesis and identify factors affecting survival.

In plain English

This study used US SEER cancer registry data on 1998 patients with histologically confirmed primary peritoneal mesothelioma (cancer of the abdominal lining) diagnosed from 1975 to 2016. It did not examine asbestos or any other exposure. Mean age at diagnosis was 69 years; 56.2% were male and 90.4% Caucasian. Tumor grade, size and histological type were mostly unrecorded; where type was recorded, epithelioid was most common. Chemotherapy was recorded for 50.6% of patients, surgery for 29.2% and radiation for 1.5%. Five-year survival was 20.3% (±1.1) overall, 43% (±5.9) among surgery patients, 25.9% (±8.4) among the 29 radiation patients and 18.7% (±1.6) among chemotherapy patients. The article does not define the ± figures, and whether treatments were combined was unknown. In a multivariable analysis, poor differentiation, tumor size over 4 cm, Caucasian race and distant spread were linked with higher odds of death. The authors concluded that surgery with heated intraperitoneal chemotherapy is optimum for fit patients without spread outside the peritoneal cavity, with systemic chemotherapy an option for patients unsuited to surgery and radiation of limited role. They called for a registry enrolling all such patients.

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: Retrospective population-based study of US cancer registry (SEER) data
• Who was studied: 1998 patients with histologically proven primary peritoneal mesothelioma recorded in the SEER database, 1975 to 2016. Patients without histological confirmation and in situ cancers were excluded.
• Exposure: Not studied. No asbestos or other exposure data were analyzed. The variables examined were age, gender, race, tumor stage and type of treatment. Asbestos is mentioned only in the introduction and discussion, citing other studies.
• Main results:
  • Patient characteristics: 1122 of 1998 (56.2%) were male and 876 (43.8%) female. The mean age at diagnosis was 69 ± 13 years.
  • Race: 1806 patients (90.4%) were Caucasian.
  • Histological type was not specified for 1266 patients (63.4%). Where it was specified, epithelioid was most common (616 patients; 30.8%).
  • Disease extent was unknown for 889 patients (44.50%). Where it was known, distant spread was most common (591 patients; 29.60%).
  • Treatment: chemotherapy 1010 patients (50.6%), surgical resection 584 (29.2%), radiation 29 (1.5%). Treatment data were missing for 375 patients (18.7%).
  • Five-year survival for the whole cohort was 20.3% (±1.1).
  • Five-year survival by treatment group: 43% (±5.9) for surgery, 25.9% (±8.4) for radiotherapy and 18.7% (±1.6) for chemotherapy. The article does not say what the ± figures measure. The authors later stated that the surgery advantage was not statistically significant.
  • Multivariable analysis linked four factors with increased mortality: poor differentiation (OR 4.2, CI 3.3 to 4.9), tumor size over 4 cm (OR 3.9, CI 3.2 to 4.5), Caucasian race (OR 2.9, CI 2.6 to 4.4) and distant SEER stage (OR 2.5, CI 1.1 to 3.2).
• The authors' conclusion: The authors concluded that surgical resection and HIPEC offer optimum management, that systemic chemotherapy is an option for nonsurgical candidates, and that radiation has a limited role. In the discussion they limit the surgery-plus-HIPEC recommendation to fit patients without extraperitoneal spread, meaning no spread outside the peritoneal cavity. They suggested an international registry enrolling all patients with this disease.
• Limitations the authors state:
  • SEER did not record the timing or type of chemotherapy (HIPEC vs systemic), the specific agents, the extent of surgery, or radiotherapy dosing.
  • The authors did not know whether each treatment was used alone or in combination.
  • Factors such as socioeconomic status, performance status, comorbidities, epithelioid subclassification and peritoneal cancer index are not coded correctly in SEER.
  • Side effects and complications of treatment were not available.

Topics

Medical terms in this study, explained in our Lexicon: Peritoneal Mesothelioma, SEER, Peritoneum, Prognosis, Epidemiology, Multivariate Analysis, Mesothelioma, Chemotherapy.

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