Angiosarcoma in fluids

A pathologist looking at fluid drained from the chest, heart sac, or abdomen can occasionally be seeing angiosarcoma, a rare cancer of blood-vessel cells, not the far more common carcinoma. A 2025 Cancer Cytopathology study described how those cells appeared in 22 fluid specimens. (acsjournals.onlinelibrary.wiley.com) The study, from The University of Texas MD Anderson Cancer Center, reviewed 22 patients with angiosarcoma involving pleural fluid in 17 cases, pericardial fluid in two, ascites in two, and a liver cyst fluid in one. All 22 patients already had an angiosarcoma diagnosis, and 10 of them, or 45%, had prior radiation exposure. (acsjournals.onlinelibrary.wiley.com) Most samples were sparse: 73% had low cellularity, meaning there were few tumor cells on the slide. Even so, the authors reported clusters of epithelioid cells in 91% of cases, single epithelioid cells in 55%, spindled cells in 36%, and prominent nucleoli in 100%. (acsjournals.onlinelibrary.wiley.com) Effusion cytology is the lab practice of examining free-floating cells in body fluids, and it is often used to decide whether an effusion is benign or caused by cancer. The International System for Reporting Serous Fluid Cytopathology, published in December 2020, set a five-tier framework for those reports: nondiagnostic, negative for malignancy, atypia of undetermined significance, suspicious for malignancy, and malignant. (xiahepublishing.com) That framework does not make rare tumors easy to spot. A 2025 open-access case series and literature review said angiosarcoma in malignant effusions is uncommon and can overlap cytologically with metastatic adenocarcinoma, because vessel-forming spaces can mimic gland formation. (pmc.ncbi.nlm.nih.gov) The MD Anderson group found several clues that can push a reviewer toward angiosarcoma instead of a more common epithelial cancer. Endothelial wrapping, a pattern in which tumor cells appear to cuff around other cells, was seen in 73% of cases, while intracytoplasmic lumina appeared in 18%, hemophagocytosis in 9%, and lumina containing cells in 5%. (acsjournals.onlinelibrary.wiley.com) The problem is that the most distinctive vascular features were often absent in the sparsest samples. The authors said low-cellularity specimens usually lacked vasoformative features, which increases the risk that a pathologist sees only atypical malignant cells without the patterns that point to a vascular tumor. (acsjournals.onlinelibrary.wiley.com) Sarcomas overall are rare in these specimens. An editorial in Cancer Cytopathology said sarcomas account for less than 1% of malignant effusions sent for pathologic evaluation, and noted that effusion samples are often hypocellular and harder to work up with extra tests such as immunohistochemistry. (acsjournals.onlinelibrary.wiley.com) The clinical course in the angiosarcoma fluid study was short once tumor cells reached the fluid. The average interval from the first positive fluid specimen to death was 141 days, and the average interval from the primary diagnosis to cavity-fluid involvement was 616 days. (acsjournals.onlinelibrary.wiley.com) That is why a free, openly available paper on slide-level features gets attention in cytopathology circles. For the people screening effusions, the practical message is narrow and concrete: in a thinly cellular fluid with epithelioid malignant cells, prominent nucleoli, and even subtle vascular hints, angiosarcoma belongs on the list. (acsjournals.onlinelibrary.wiley.com)