PLEKHH2-ALK: A Novel In-frame Fusion With Durable Response to Alectinib: Utilizing RNA Sequencing in Search for Hidden Gene Fusions Susceptible to Targeted Therapy

ALK-Rearranged Epithelioid and Spindle Cell Neoplasm of the Sinonasal Tract

Anaplastic lymphoma kinase (ALK)-rearranged mesenchymal neoplasms (non-inflammatory myofibroblastic tumor and non-epithelioid fibrous histiocytoma) have been recently described which tend to occur in the superficial and deep soft tissues. Occurrence as a primary sinonasal neoplasm has not been reported thus far. Herein, we describe the first case of sinonasal ALK-rearranged mesenchymal tumor that harbored remarkable epithelioid and spindle cell morphology. The tumor affected a 40-year-old man who presented with flu-like symptoms and was thought to have influenza A. However, computed tomography demonstrated a nasal polypoid lesion causing curvature of the nasal septum. Histological examination revealed a heterogeneous tumor composed of round to epithelioid cells with foci of spindle cells. The tumor cells exhibited moderate pleomorphism and mitotic activity. By immunohistochemistry, they showed diffuse staining of CD34, S100, ALK (D5F3) and CD30. Fluorescence in situ hybridization analysis demonstrated ALK rearrangement. Subsequent next-generation sequencing (RNA-seq) identified a rare PLEKHH2exon6::ALKexon20 fusion. This study further demonstrates the importance of molecular profiling in identifying kinase fusion-positive soft tissue tumors, particularly for those that arise at unusual sites and display atypical cytomorphology.

ALK-rearranged, CD34-positive spindle cell neoplasms resembling dermatofibrosarcoma protuberans: a study of seven cases

AIMS

The majority of dermatofibrosarcoma protuberans (DFSP) harbour PDGFB or PDGFD rearrangements. We encountered ALK expression/rearrangement in a PDGFB/D-negative CD34-positive spindle cell neoplasm with features similar to DFSP, prompting evaluation of ALK-rearrangements in DFSP and plaque-like CD34-positive dermal fibroma (P-LDF).

METHODS AND RESULTS

We searched the archives of academic institutions for cases previously coded as DFSP and P-LDF. NGS-naïve or PDGFB-negative DFSP were screened for ALK (clone D5F3) expression by immunohistochemistry. NGS or ALK FISH was performed on ALK-positive cases. Methylome profiling studies were performed and compared with conventional DFSP. One case of "DFSP" and two "P-LDF" with ALK expression were identified from the archives, while four cases were detected prospectively. These seven cases (6F:1M; 8 months to 76 years) arose in the dermis of the arm (two), scalp, eyelid, thigh, abdomen, and shoulder and ranged from 0.4 to 4.2 cm. Tumours were composed of spindled cells and displayed a storiform growth pattern. Cytologic atypia was absent, and mitotic figures were scarce (0-2/10 HPFs, high power fields). The lesional cells were diffusely positive for CD34 and ALK and negative for S100 protein. By NGS (n = 5), ALK fusion partners included DCTN1 (2), PLEKHH2, and CLIP2 in DFSP-like cases and FLNA in P-LDF-like lesions. ALK FISH was positive in one (of two) cases previously labelled P-LDF. Methylome profiling of two (of three) ALK-rearranged DFSP-like tumours showed clustering with conventional DFSP in the UMAP dimension reduction plot. To date, no tumour has recurred (n = 2; 26, 27 months).

CONCLUSION

We describe a cohort of novel ALK-rearranged tumours with morphologic features similar to DFSP.

PLEKHH2 binds β-arrestin1 through its FERM domain, activates FAK/PI3K/AKT phosphorylation, and promotes the malignant phenotype of non-small cell lung cancer

PLEKHH2 is an important FERM domain containing-protein. However, the role of PLEKHH2 in human solid tumors has not been reported yet. We report that PLEKHH2 showed enhanced cytoplasmic expression in non-small cell lung cancer (NSCLC). Its overexpression was positively correlated with high TNM stage, low differentiation, lymphatic node metastasis, and poor prognosis. In A549 and H1299 cells, high expression of PLEKHH2 significantly promoted cell proliferation, migration, invasion, and increased the expression of proliferation- and invasion-related proteins. It also enhanced the phosphorylation of FAK and promoted the activity of the PI3K/AKT pathway. Immunofluorescence and co-immunoprecipitation analyses were performed to elucidate the molecular mechanism underlying PLEKHH2-mediated regulation of proliferation and invasion in lung cancer cells. Upon transfection of full length PLEKHH2 or its FERM domain, we observed enhanced binding of PLEKHH2 to β-arrestin1, whereas FAK- β-arrestin1 binding was diminished and this led to an increase in FAK phosphorylation. PLEKHH2-mutant plasmids without the FERM domain could not effectively promote its binding to β-arrestin1, activation of FAK phosphorylation, PI3K/AKT activation, or the malignant phenotype. Our findings suggested that PLEKHH2 is an important oncogene in NSCLC. PLEKHH2 binding to β-arrestin1 through the FERM domain competitively inhibits β-arrestin1 binding to FAK, which causes the dissociation of FAK from the FAK-β-arrestin1 complex. Furthermore, the dissociation of FAK promotes its autophosphorylation, activates the PI3K/AKT signaling pathway, and subsequently promotes lung cancer cell proliferation, migration, and invasion. These results provide evidence for the potential use of PLEKHH2 inhibition as an anticancer therapy.

S100 and CD34 Expressing Mesenchymal Neoplasm With Rare PLEKHH2::ALK Fusion and Response to ALK Inhibition

The PLEKHH2::ALK fusion is a rarely reported gene fusion identified predominantly in lung adenocarcinomas. Tumors with this fusion have been reported to be of durable response to ALK inhibitors. We herein present the case of a 21-year-old woman with a histomorphologically heterogenous mesenchymal neoplasm of the pelvis, expressing both s100 and CD34, with subsequently identified PLEKHH2::ALK fusion. To our knowledge, only a single mesenchymal neoplasm with this gene fusion has been previously reported. We propose that this tumor represents one with a novel ALK fusion in the emerging family of s100 and CD34 expressing mesenchymal neoplasms with oncogenic kinase alterations akin to NTRK -rearranged mesenchymal neoplasms, rather than inflammatory myofibroblastic tumor. Importantly, this tumor demonstrated a significant response to the ALK inhibitor brigatinib.

Pediatric Non-Myofibroblastic Primitive Spindle Cell Tumors with ALK Gene Rearrangements and Response to Crizotinib

We describe two poorly differentiated, non-myofibroblastic (SMA-, S100+, CD34±), spindle cell neoplasms with immunohistochemical positivity for ALK and with ALK gene rearrangements leading to PLEKHH2::ALK and CLTC::ALK fusions, respectively. ALK protein overexpression and/or gene fusions should be evaluated in poorly differentiated spindle cell neoplasms, even when there is an absence of a myofibroblastic phenotype. A positive ALK evaluation has therapeutic implications as both tumors responded to single-agent treatment with the tyrosine kinase inhibitor crizotinib.

An overview of alectinib hydrochloride as a treatment option for ALK positive non-small cell lung cancer

Introduction: Alectinib is a second-generation inhibitor of anaplastic lymphoma kinase (ALK) and RET. Phase III clinical trials have established its superiority to crizotinib in the first-line ALK inhibitor-naïve setting. Studies also support its use over chemotherapy in the post-crizotinib setting. It is currently one of several FDA- and EMA-approved ALK inhibitors, and it is listed as a preferred initial therapy for treatment-naïve ALK-positive non-small cell lung cancer (NSCLC).Areas covered: Herein, the authors provide the reader with details of the chemical structure, pharmacologic properties, resistance mutations, phase I, II, and III clinical trials, and safety profile of alectinib. Furthermore, the authors provide the reader with the expert opinion and future perspectives on the drug.Expert opinion: Alectinib compares favorably to other second-generation ALK inhibitors with regards to safety, tolerability, and efficacy. Based on currently available data, it is an appropriate first-line option. Ongoing studies will better resolve the ideal sequencing of ALK inhibitors in the treatment of ALK-positive NSCLC.