How to Diagnose Anaplastic Large Cell Lymphoma on Cytological Samples? A Series with Emphasis on Diagnostic Clue and Pitfalls

Introduction: Anaplastic large cell lymphoma (ALCL) is a rare mature T-cell non-Hodgkin's lymphoma characterized by large and pleomorphic neoplastic CD30-positive T cells. ALCL includes different subtypes with different clinical and biological features: systemic ALCL, primary cutaneous ALCL, breast implant-associated ALCL (BIA-ALCL). Anaplastic lymphoma kinase (ALK) is overexpressed and rearranged in some systemic cases. Diagnosis of ALCL may be challenging on cytological samples, but the correct diagnosis is mandatory for the management of the patient. Methods: A retrospective series of 12 ALCLs diagnosed by cytology is reported. Cytological samples included lymph nodes and skin lesions fine needle aspiration cytology, peritoneal effusion, and periprosthetic fluid. Microscopic evaluation was performed on direct smears, cell-block sections, and cytocentrifugated slides. Immunocytochemistry was performed on cell-block sections, direct smears, and cytocentrifugated slides. Molecular evaluation by fluorescent in-situ hybridization (FISH) was performed on cell-block sections. Results: The series included 4 ALK+ ALCLs, 5 ALK- ALCLs, and 3 BIA-ALCLs. FNAC was performed on lymph nodes in 8 cases and on skin lesion in 1 case. In this last case, a peritoneal effusion was also evaluated. Breast periprosthetic fluids were evaluated in 3 cases. A large immunocytochemical panel was performed in each case, and FISH in 3 cases, demonstrating ALK rearrangement in a case of ALK+ ALCL. A final diagnosis was rendered in all cases. In the case of skin lesion, the differential diagnosis between systemic ALCL and primary cutaneous ALCL was possible. Conclusion: The cytological diagnosis of ALCL may be challenging, and the proper management of the collected sample is mandatory. The rapid on-site evaluation and the realization of a cell block are strongly recommended. Immunocytochemistry is mandatory for the diagnosis and a large antibodies panel is needed as differential diagnosis includes many different neoplasms. FISH may be useful to evaluate ALK rearrangements. When properly managed, cytology can lead to a reliable final diagnosis of ALCL