Atypical mesothelial cells associated with eosinophilic pleural effusions: nuclear DNA content and immunocytochemical staining reaction with epithelial markers

Cytomorphological changes induced by intraperitoneal chemotherapy present important diagnostic pitfalls in peritoneal fluid cytology

OBJECTIVE

Intraperitoneal chemotherapy (IP ChT) is an emerging modality in the treatment of advanced gastric adenocarcinoma with peritoneal disease. Cytological evaluation of peritoneal fluid specimens from patients undergoing IP ChT is important in clinical management. However, direct intraperitoneal exposure to chemotherapeutic agents induces cytomorphological changes in benign constituents of peritoneal fluid, presenting particular challenges to accurate cytological interpretation. These morphological changes have not been well characterised in the literature. We systematically reviewed the cytomorphological features in immunocytochemically-confirmed positive and negative IP ChT peritoneal fluid samples to elucidate the degree of morphological overlap between malignant and reactive cells.

METHODS

We reviewed 39 peritoneal fluid samples of patients treated with IP ChT, and scored specific cytomorphological parameters of both benign and malignant cells with the aid of relevant immunocytochemical interrogation.

RESULTS

The present findings show a significant degree of morphological overlap between reactive and malignant cells. Abnormal, "exploding" mitotic figures, nuclear membrane irregularities, multi-nucleation and cytoplasmic vacuolation were commonly observed in negative fluid specimens. The most helpful feature that favoured malignant cells was the increased nuclear-to-cytoplasmic ratio. A background inflammatory milieu of eosinophils and/or neutrophils was seen in 45-58% of post IP ChT peritoneal fluid specimens. The presence of pseudoparakeratotic cells, a novel observation in post IP ChT fluid specimens is also described.

CONCLUSIONS

The extent of reactive cytomorphological anomalies arising from treatment with IP ChT poses unique diagnostic challenges and may prompt a malignant or 'atypical' diagnosis in benign reactive samples.

Hyperdiploidy and apparent aneusomy in mesothelial cells from non-malignant effusions as detected by fluorescence in situ hybridization (FISH)

Interphase cytogenetics by fluorescence in situ hybridization (FISH) can be used to detect malignant cells characterized by chromosomal aneuploidy. However, apparent aneusomy in normal "control" tissues has to be considered when using FISH as diagnostic tool. In effusions as model tissue exposed to metastasis, the definition of cut-off levels for background aneusomy by FISH was aimed in this study. Using centromeric probes representing chromosomes 7, 8, 11, 12, 17 and 18, extensive chromosome copy number enumeration by single-color FISH analysis was performed in pleural and ascitic effusions derived from 15 patients with various, non-malignant diseases. In all effusions, cells with gain of hybridization signals for several or all chromosomes tested were found (in up to 1.94% of cells). A consistent finding was high grade hyperdiploidy (>4 centromeric signals). Mesothelial elements mainly contributed to hyperdiploidy in effusions, as demonstrated by a combined analysis of FISH and immunocytochemistry with staining for cytokeratin. Dual-color FISH analysis showed that hyperdiploidy was predominantly corresponding to polyploidization; however, there were always minor cell populations classified as aneuploid by dual-color FISH. In conclusion, stringent criteria have to be applied to distinguish malignancy-related aneuploidy from background aneusomy by FISH.