lymphohistiocytoid mesothelioma
Lymphohistiocytoid mesothelioma is a rare variant of mesothelioma that may simulate an inflammatory process or malignant lymphoma.
The malignant mesothelial cells have features resembling histiocytes and are submerged in a mixed infiltrate that includes true benign histiocytes and small lymphocytes.
The neoplastic cells may be difficult to identify in H&E sections as they are poorly cohesive.
Like histiocytes, their nuclei tend to be oval and irregular, but with greater hyperchromasia and more prominent nucleoli.
In small biopsy specimens, the diagnosis may be extremely difficult unless there is a strong suspicion of mesothelioma.
The same rules apply as with more typical mesotheliomas, and infiltration into fat is a useful feature, provided the specimens are of sufficient size to appreciate this.
Careful evaluation of the immunohistochemistry demonstrates a population of CD68+ histiocytes that are distinct from the mesothelial cells, which are positive for EMA, broad-spectrum CKs such as AE1/3 and MNF116, CK5/6 and calretinin.
The small lymphocytes are predominantly CD8+ T cells that are positive for the cytotoxic granule markers TIA-1, granzyme and perforin.
In a large series, the prognosis of this variant has been shown to be similar to epithelioid mesothelioma.
See also
mesotheliomas