Pulmonary adenocarcinoma with signet ring features: Detailed cytomorphologic analysis

Background Signet ring cell feature in lung adenocarcinoma is no longer considered a distinct subtype, but as a cytologic change that may occur in association with multiple histological patterns. Cases with signet ring cells show a strong association with Anaplastic Lymphoma Kinase (ALK) gene fusions and solid pattern. Methods The cytomorphological findings of pulmonary adenocarcinoma with signet ring features (PASRF) was studied. Cases of pulmonary adenocarcinoma which showed presence of signet ring cells either on cytology or histology were included in the study. Results Out of 218 pulmonary adenocarcinomas diagnosed during the study period, 11 cases showed presence of signet ring cells (11/218). Out of the 11 cases, 7 had paired histology and cytology available, while the remaining 4 did not have a corresponding cytology sample. Majority of the cases (6/11) showed signet ring cells in more than 90% of the tumor area. All cases showed solid growth pattern. TTF‐1 was positive in all the cases. Immunopositivity for ALK was seen in seven cases. The cytology smears showed single cells and clusters of signet ring cells, with either intracytoplasmic mucin vacuole and eccentric nucleus or histiocyte‐like finely vacuolated cytoplasm with round nucleus and prominent nucleoli, the latter resembling alveolar macrophages. Conclusion PASRF is commonly associated with a solid histologic pattern. Cases with predominant histiocyte‐like pattern may be misdiagnosed on cytology; hence a high index of suspicion is required for an accurate diagnosis. Diagn. Cytopathol. 2016;44:607–611. © 2016 Wiley Periodicals, Inc.