[84] ALK Immunoexpression and Gene Status in Rhabdomyosarcomas

Akihiko Yoshida, Susumu Wakai, Tetsuo Ushiku, Koji Tsuta, Atsushi Makimoto, Masashi Fukayama, Koh Furuta, Hitoshi Tsuda, Tatsuhiro Shibata. National Cancer Center, Tokyo, Japan; The University of Tokyo, Tokyo, Japan

Background: Anaplastic lymphoma kinase (ALK) is overexpressed via gene alteration in a number of neoplasms, and it has recently become a promising target of a specific inhibitor. Although ALK expression is immunohistochemically detectable, recent studies on ALK-rearranged lung cancer showed that staining according to the conventional protocol is unreliable. As a result, several sensitive staining methods have been developed. ALK expression in rhabdomyosarcoma (RMS) has been reported in a few studies, but sensitive staining method has not been tested. In addition, the genetic basis of ALK expression in RMS remains poorly understood.
Design: We performed a previously validated (Am J Surg Pathol. 2011:35;1224-38) sensitive ALK immunostaining for 106 RMSs (35 embryonal, 56 alveolar [ARMS], 7 pleomorphic, 8 adult-spindle/sclerosing). The staining results were correlated with the clinicopathological findings and FOXO1 status studied by FISH. Selected cases were also tested for ALK rearrangement (with ALK break-apart probes) and copy number change (with ALK/CEN2 probes) by using FISH and for ALK somatic mutation by PCR and sequencing.
Results: ALK expression was identified in 2 (5.7%) embryonal, 38 (68%) alveolar, and 0 (0%) pleomorphic and spindle/sclerosing types. Staining was diffuse (>50%) in most (90%) positive cases. ALK-positive ARMS more commonly presented with metastasis than ALK-negative ARMS (p < 0.01). FOXO1 rearrangement was present in 38/43 of the ARMS, and all the 5 FOXO1-wild-type ARMSs were ALK-negative. ALK rearrangement was absent in all the tested ALK-positive cases (0/12). Gene amplification (median ALK/CEN2 ≥ 2), low-level gain (2 > median ALK/CEN2 > 1), and high polysomy (≥ 4 ALK copies in >40% of cells) were identified in 1, 3, and 9 of the 48 successfully studied cases, respectively, and these were all positive for ALK expression. Mutation was present in 1 of the 19 successfully studied cases, but the mutated tumor was an ALK-negative embryonal type.
Conclusions: ALK expression is relatively specific to the alveolar type and seems limited to the FOXO1-rearranged subset. Positive staining in ARMS may indicate a subgroup with a proclivity to early metastasis. ALK copy number change is related to protein expression, but this was observed in only a subset (∼30%) of the immunopositive cases. ALK gene rearrangement and mutation do not seem to play a major role in RMS. These data may help to preselect patients with RMSs for ALK-targeted therapy in future clinical trials.
Category: Bone & Soft Tissue

Tuesday, March 20, 2012 8:30 AM

Platform Session: Section G, Tuesday Morning


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