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Inflammatory myofibroblastic tumors (IMTs) are intermediate-grade mesenchymal neoplasms commonly characterized by chromosomal rearrangements causing constitutive activation of anaplastic lymphoma kinase (ALK) and/or ALK mutations causing reduced sensitivity to ALK tyrosine kinase inhibitors (TKI). We present a patient with an IMT who initially responded to first-line alectinib, but who later suffered disease relapse and presently survives with moderate residual disease after receiving second-line lorlatinib. Biopsy specimens were analyzed using next generation sequencing (DNA-seq and RNA-seq) and reverse phase protein microarray (RPPA) as part of an institutional Molecular Tumor Board (MTB) study. An EML4-ALK rearrangement and EGFR activation (pEGFRY1068) were present in both the primary and recurrent tumors, while a secondary ALK I1171N mutation was exclusive to the latter. EGFR signaling in the background of a secondary ALK mutation is correlated with reduced ALK TKI sensitivity in vitro, implicating an important mechanism of drug resistance development in this patient. The RPPA results also critically demonstrate that ALK signaling (ALKY1604) was not activated in the recurrent tumor, thereby indicating that standard-of-care use of third- or fourth-line ALK TKI would not likely be efficacious or durable. These results underscore the importance of real-time clinical integration of functional protein drug target activation data with NGS in the MTB setting for improving selection of patient-tailored therapy.

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e16299 Background: Pancreatic adenocarcinoma (PDAC) is associated with poor survival and low response rates to available therapies, warranting a critical need for new treatment paradigms. Enrichment of tumor epithelium via laser microdissection (LMD) prior to reverse phase protein array (RPPA) analysis allows for the quantitative measurement and functional assessment of the activation state of protein drug targets. As part of an IRB-approved Molecular Tumor Board study at Inova Schar Cancer Institute, we harvested enriched tumor epithelium using LMD to support CLIA-based RPPA analysis of patients with pancreatic, breast, and other solid tumor malignancies to examine quantitative expression and activation (phosphorylation) of HER-2/3 and other known cancer-related pathways. Methods: Formalin fixed paraffin embedded (FFPE) primary and/or metastatic tumor biopsy specimens were obtained from 14 patients with PDAC, 14 patients with breast cancer, and 40 patients with other solid tumor malignancies. Tumor epithelium (5-10 µm2) was enriched via LMD prior to RPPA analysis for quantification of HER-2Total and phosphorylated (p)HER-2Y1248 and (p)HER-3Y1289 abundances as part of a 32-marker, CLIA-based RPPA panel examining the total and phosphoprotein abundances of targets with known relevance in solid tumors. Next generation sequencing (NGS; DNA-seq and RNA-seq) was performed on remaining tissue from each specimen. Fisher’s Exact test was used to compare activated HER2Total, pHER2Y1248 and pHER3Y1289. Results: RPPA analysis of LMD enriched tumor samples revealed significant HER-2Total expression in patients with PDAC vs other solid tumors (p=0.0112), with HER-2Total levels comparable to those measured in patients with breast cancer (p=0.0962). The mean HER-2Total abundances in PDAC, breast, and all other solid tumor malignancies were 1.6, 1.3, and 0.9, respectively. Activated pHER-2Y1248 and pHER-3Y1289 abundances did not differ between patients with PDAC vs all other solid tumors or between patients with PDAC vs breast cancer (p>0.05). RNA-seq analysis revealed ERBB2 overexpression in four of the 14 PDAC patients, while ERBB2 amplification by DNA-seq was not observed in any of the PDAC cases. Conclusions: HER-2 expression is not routinely evaluated in clinical practice in PDAC, but our results show higher median expression in PDAC than our solid tumor cohort, with nearly 50% of PDAC cases having total HER2 expression of 2+ or above. Our results may have clinical implications, especially as new classes of HER2 antibody drug conjugates are considered for patients with HER2 non amplified tumors across organ sites, and justify further investigation in a larger cohort. Clinical trial information: U20-11-4308 . [Table: see text]