"Single-cell pattern" adenocarcinoma cells in effusion cytology: A nightmare for cytologists.

Single-cell pattern adenocarcinoma cells, unlike cohesive morphology, are difficult to detect with low magnification screening under the microscope. These single cells hide among background cells and are often confused with reactive mesothelial cells, making them one of the most challenging patterns for cytologists to identify with confidence.

A study by Guleria et al. (2021) found that among 103 cases reported as suspicious or positive for malignancy on pleural fluid cytology, 29 showed a predominant single-cell pattern. Of these, nearly half (44.8%) were primary lung carcinoma, while the remainder were metastases originating from the ovary, breast, stomach, lymphoma, and Ewing's sarcoma. The takeaway is clear: single-cell pattern pulmonary adenocarcinoma occurs far more frequently than conventional wisdom suggests.