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Page 10 of 13 Farkas et al. J Cancer Metastasis Treat 2022;8:37 https://dx.doi.org/10.20517/2394-4722.2022.89

[11]
used to diagnose mesothelioma in the pleura . The adaptation for these panels is made to delineate the
various potential origins of peritoneal neoplasms. Pleural malignancies generally have a pulmonary origin,
but peritoneal malignancies can originate from the ovaries, fallopian tubes, stomach, pancreas, colon, and
kidney, and includes metastases from outside the peritoneal cavity (breast, lung carcinomas, etc.).

Peritoneal mesothelioma has somewhat been an orphan disease, with most publications pertaining to
mesothelioma focusing on pleural mesothelioma. Excitingly, groups have recently begun to seriously look at
the diagnosis and classification of peritoneal mesothelioma [57,60] . Our group recently published an article
highlighting that many of the same pathologic parameters observed in the thoracic cavity can be applied to
peritoneal mesothelioma with similar results . This is an emerging area of exploration, and new and
[57]
exciting research on this disease will certainly be published in the coming years.

MESOTHELIOMA IN SITU
Mesothelioma in situ (MIS) is the growth of malignant mesothelial cells, either as a monolayer or small
papillary growth, without invasion of the underlying tissue and with corresponding negative radiology
[8]
findings . MIS, as a concept, is quite old, but could not be proven definitively as a malignant precursor,
leading to the controversy surrounding its definition and diagnosis . In recent years, especially in patients
[61]
with nonresolving unexplained pleural effusions, loss of BAP1 and/or MTAP by immunohistochemistry, or
identification of homozygous deletion of CDKN2A by FISH in noninvasive mesothelial cells, has proven
that one can detect signatures of malignancy in mesothelial cells prior to the development of invasive diffuse
[8]
mesothelioma [62-66] . MIS is now accepted as an entity in the WHO . The ability to diagnose MIS is very
recent; thus, this diagnosis will most likely have implications in pleural fluid cytology specmens . The
[67]
biggest question now is what the oncologist or surgeon should do if this diagnosis is made . This is a
[68]
question that remains to be answered. As cases continue to be reported, mesothelioma pathologists will
continue to study this disease.

CONCLUSION
Recent advancements in the field of mesothelioma have led to robust prognostic grading schemes that are
now included in the routine reporting of mesothelioma specimens. Advancements in ancillary testing have
expanded the pathologist’s ability to diagnose mesothelioma on small biopsies and in cytology fluids. The
emergence of mesothelioma in situ as a distinct entity has the potential to change how the medical team
views mesothelioma and may provide a means to intervene earlier in the disease.

DECLARATIONS
Authors’ contributions
Made substantial contributions to conception and design of the article and performed review of literature:
Farkas JR, Sharobim M, Schulte JJ

Availability of data and materials
Not applicable.

Financial support and sponsorship
None.

Conflicts of interest
All authors declared that there are no conflicts of interest.