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BAC Slide Club Review - May 2026

The BAC May Slide Club featured a series of engaging cytology case discussions covering diagnostic pitfalls, ancillary testing, and the importance of clinicopathological correlation. The session included presentations from Sue Smith and Dr Anthony Maddox, focusing on challenging fluid and thyroid cytology cases.

Case 1: Ascitic Fluid Revealing Metastatic Breast Carcinoma

Presenter: Sue Smith, Lincolnshire Community and Hospitals NHS Group

A 54-year-old female patient presented with an ascitic fluid specimen with very limited clinical information provided. Only 10ml of pale yellow fluid was received, significantly below the recommended optimal volume for serous fluid cytology.

Initial cytospin preparations appeared relatively bland, showing mesothelial cells, macrophages and inflammatory cells. However, closer examination revealed subtle atypical features including nuclear enlargement, intracytoplasmic vacuoles and nuclear folds. The atypical population became more evident in better-fixed areas of the preparation and on Giemsa staining.

Further investigation uncovered a previous history of invasive lobular breast carcinoma with metastatic disease. A plasma-thrombin clot was prepared for immunohistochemistry. The atypical cells showed positivity for Claudin, GATA3 and ER, while TTF1 was negative, confirming metastatic breast carcinoma involving the ascitic fluid.

Key learning points:

  • Good fixation and slide preparation are critical for identifying subtle malignant features.
  • Adequate fluid volume is essential, with approximately 75ml recommended for optimal assessment.
  • Clinical history is vital in directing ancillary testing and avoiding diagnostic delays.
  • Reactive mesothelial cells can closely mimic malignant populations in poorly prepared samples.

Case 2: Reactive Pericardial Effusion Mimicking Hodgkin Lymphoma

Presenter: Dr Anthony Maddox, West Hertfordshire Teaching Hospitals NHS Trust

A 44-year-old woman presented with shortness of breath and fever. Imaging demonstrated a large anterior mediastinal mass with hilar lymphadenopathy. EBUS-guided sampling showed classical Reed–Sternberg cells positive for CD30 and CD15, confirming Hodgkin lymphoma.

During treatment, the patient later developed a pericardial effusion. Cytology showed reactive mesothelial cells, macrophages and eosinophils. Immunohistochemistry unexpectedly demonstrated strong CD30 positivity in multiple cells, initially raising concern for persistent lymphoma.

Further assessment demonstrated that the CD30-positive cells represented reactive mesothelial cells and macrophages rather than lymphoma involvement. Additional markers including calretinin and CD68 supported a reactive process. PET imaging also confirmed the effusion was non-avid and therefore unlikely to represent active lymphoma.

Key learning points:

  • CD30 is not entirely specific for Hodgkin lymphoma and may be expressed in reactive mesothelial cells and macrophages.
  • Correlation between morphology, immunohistochemistry and imaging is essential.
  • Reactive effusions during treatment can create significant diagnostic pitfalls.

Case 3: Papillary Thyroid Carcinoma on Fine Needle Aspiration

Presenter: Dr Anthony Maddox, West Hertfordshire Teaching Hospitals NHS Trust

The final case involved a 57-year-old patient with a U2/U3 thyroid lesion undergoing fine needle aspiration.

The sample demonstrated high cellularity with flat epithelial sheets, minimal colloid and subtle nuclear atypia. Features suggestive of papillary thyroid carcinoma, including dusty chromatin, nuclear grooves and intranuclear inclusions, were present but initially difficult to identify.

Careful review of both conventional smears and ThinPrep preparations eventually revealed convincing diagnostic features, allowing confirmation of papillary thyroid carcinoma.

Key learning points:

  • Papillary thyroid carcinoma can present with subtle cytological features requiring extensive slide review.
  • Architectural features and nuclear detail remain central to diagnosis.
  • Multiple FNA passes and dedicated ThinPrep samples improve the ability to perform cell block preparation and molecular testing.

Summary

The May Slide Club highlighted the value of detailed morphological assessment, high-quality specimen preparation and multidisciplinary communication in cytopathology practice. The discussions also reinforced the importance of recognising diagnostic pitfalls and integrating cytology with immunohistochemistry, imaging and clinical history.