WHO classifies these infiltrates into 5 patterns: a Common Pattern consisting of large variably-shaped cells with large nuclei that typically contain multiple nucleoli (60–70% of cases); a Small Cell Pattern consisting of small to medium-sized neoplastic cells with clear cytoplasm and "hallmark" cells that are concentrated around small blood vessels (5–10% of cases); a Lymphohistiocytic Pattern consisting of small neoplastic cells along with abundant histiocytes (10% of cases); a Hodgkins-Like Pattern in which the architecture resembles the nodular sclerosis pattern of Hodgkin lymphoma (3% of cases); and a Composite Pattern consisting of two or more of the just described patterns (15% of cases). Detection of circulating autoantibody against ALK supports the diagnosis. Individuals with low levels of these autoantibodies are at an increase risk of relapsing after treatment. Gene and molecular abnormalities
In 80–85% of cases, the ALK detected in ALK-positive ALCL is a NPM1-ALK fusion protein. It is made by a fusion of NPM1 gene, which makes nucleophosmin 1, located on the long or "q" arm of chromosome 5 at position 35 (notated as 5q35) with the ALK gene located on the short or "p" arm of chromosome 2 at position 23 (notated as 2p23) to form a chimeric gene notated as (2;5)(p23;q35). In 13% of cases ALK fuses with the TPM3 gene or in <1% of cases for each of the following genes: TFG, ATIC, CLTC, TPM4, MSN, RNF213 (also termed ALO17), MYH9, or TRAF1.
Contrary to pleomorphic adenoma, it is non recurrent. See also
Pleomorphic adenoma

References
Additional sources
Kahn, Michael A. Basic Oral and Maxillofacial Pathology. Volume 1. 2001. == External links ==