RET proto-oncogene encodes a receptor tyrosine kinase whose ligand is glial cell line-derived neurotrophic factor (GDNF), and its polymorphism at G691S juxtamembrane region (RETp) is a germline polymorphism. Cutaneous melanomas, particularly the desmoplastic subtype, are highly neurotropic; thus we sought to determine the frequency of RETp in cutaneous melanoma and its functional responsiveness to GDNF. RETp was assessed in 71 non-desmoplastic cutaneous melanomas (non-DMs) and 70 desmoplastic melanomas (DMs). Melanoma cell lines with RETp, RET wild-type (RETwt), BRAF V600E mutation (BRAFmt) or BRAF wild-type (BRAFwt) were assessed for functional activity. RETp frequency was significantly higher in DMs (61%) than in non-DMs (31%, P<0.001). BRAFmt was detected in only 11% of DMs. GDNF stimulation significantly amplified cell proliferation, migration, and invasion in RETp, but not in RETwt melanoma cells. GDNF stimulation of RETp cell lines enhanced phosphorylation of extracellular signal-regulated kinase (ERK) and Akt of the RET-RAS-RAF-ERK and RET-phosphatidylinositol 3-kinase (PI3K)-Akt pathways, respectively. GDNF response of RETp cells in signal transduction and other functional studies were not affected by BRAFmt. The study demonstrates that RETp are frequently found in cutaneous melanoma, particularly desmoplastic subtypes, and responds to GDNF inducing events favorable for tumor progression.

Retroperitoneal sarcoma, regardless of the histopathologic grade of malignancy, has a high incidence of local recurrence that is usually fatal. Surgical resection is mandatory and resectability may be improved by a midline transabdominal approach. However, even with total tumor excision, recurrence is high. A preliminary study, combining resection and preoperative adriamycin, found to be effective for established disease, suggests potentially improved prognosis. Further clinical trials employing combined with adjuvant chemotherapy are warranted.

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