Expression of PAX3 Distinguishes Biphenotypic Sinonasal Sarcoma From Histologic Mimics.

Biphenotypic sinonasal sarcoma (BSNS) is a distinctive, anatomically restricted, low-grade spindle cell sarcoma that shows considerable histologic overlap with other cellular spindle cell neoplasms. This tumor type shows both myogenic and neural differentiation, which can be demonstrated by immunohistochemistry; however, the available diagnostic markers are relatively nonspecific. BSNS is characterized by PAX3 rearrangements, with MAML3 as the most common fusion partner. Our aim was to determine whether immunohistochemistry using a monoclonal PAX3 antibody could distinguish BSNS from potential histologic mimics, as well as to evaluate a widely available polyclonal PAX8 antibody, which is known to cross-react with other paired box transcription factor family members. Immunohistochemistry for PAX3 and PAX8 was performed on whole sections of 15 BSNS (10 with confirmed PAX3 rearrangement) and 10 cases each of the following histologic mimics: malignant peripheral nerve sheath tumor, monophasic synovial sarcoma, spindle cell rhabdomyosarcoma (RMS), solitary fibrous tumor, sinonasal hemangiopericytoma, and cellular schwannoma, as well as alveolar RMS (which harbors PAX3 or PAX7 gene rearrangements). BSNS showed consistent expression of PAX3 (15/15), all multifocal-to-diffuse and most with moderate-to-strong intensity of staining. One single case of spindle cell RMS showed PAX3 expression (1/10), and all other histologic mimics were completely PAX3-negative. In contrast, nuclear staining for PAX8 was present in all 15 BSNS, 7/10 malignant peripheral nerve sheath tumor, 3/10 cellular schwannomas, 2/10 sinonasal hemangiopericytomas, 1/10 synovial sarcoma, 1 spindle cell RMS, and 1 solitary fibrous tumor. All cases of alveolar RMS were positive for PAX8, and most were also positive for PAX3 (8/10). Immunohistochemical expression of PAX3 is highly sensitive (100%) and specific (98%) for BSNS. A polyclonal PAX8 antibody also stains BSNS (likely due to cross-reactivity with PAX3) but has much lower specificity (75%), with frequent expression in numerous mimics.

Loss of MicroRNA-489-3p promotes osteosarcoma metastasis by activating PAX3-MET pathway.

Osteosarcoma (OS) remains one deadly disease for many affected patients. MicroRNAs (miRNAs) are thought to have an important role in tumor metastasis by regulating diverse cellular pathways. Here, we describe the function and regulation network of miR-489-3p in osteosarcoma (OS) metastasis. MiR-489-3p expression was downregulated in OS cells especially in high metastatic potential cells and was also significantly decreased in metastatic lesions compared with their corresponding primary tumor samples. Both gain- and loss-of-function studies confirmed that miR-489-3p significantly suppressed OS cell invasion and metastasis both in vitro and in vivo. Mechanistically, paired box gene 3 (PAX3) was identified as a functional target of miR-489-3p in OS cells. MiR-489-3p inhibited OS metastasis by negatively regulating expression of PAX3. In addition, PAX3 expression was markedly higher in OS tissues than in adjacent non-cancerous tissues. Transwell assays and in vivo metastasis assays demonstrated that overexpression of PAX3 significantly promoted the invasiveness and pulmonary metastasis of OS cells. On the other hand, downregulation of PAX3 markedly reduced cell metastatic potential. Mechanistic investigations indicated that prometastasis function of PAX3 was mediated by upregulating downstream target MET tyrosine kinase receptor. In conclusion, our results reveal that miR-489-3p-PAX3-MET signaling is critical to OS metastasis. Targeting the pathway described here may open new therapeutic prospects to restrict the metastatic potential of OS. © 2016 Wiley Periodicals, Inc.