USMLE题库Dermatology1-10.pptx

Dermatology 题库 Q 1 A 56-year-old male is brought to the emergency department with new-onset tonic-clonic seizures. His past medical history is insignificant. MRI of the brain reveals a round 1.6 cm mass in the right temporal lobe. After initial evaluation, a stereotactic biopsy of the mass is obtained. The biopsy results show a neoplastic tissue containing a mutation in the gene that encodes BRAF, a protein kinase. The point mutation results in a substitution of glutamic acid for valine at position 600 of the protein. Which of the following is the most likely diagnosis? Glioblastoma Melanoma Prostate cancer Renal cell carcinoma Small cell lung cancer A 1 Correct answer: B The main environmental risk factor for cutaneous melanoma is increased exposure to ultraviolet radiation. Exposure to both solar and tanning-bed ultraviolet sources increases the risk of developing cutaneous melanoma, as ultraviolet radiation can cause malignant transformation of melanocytes. This risk is also increased by mutations in specific genetic factors, most commonly tumor suppressor genes and various oncogenes. BRAF is a protein kinase involved in activating the signaling pathways of melanocyte proliferation, and the BRAF mutation V600E (valine replaced by glutamate) is seen in 40-60% of patients with melanoma. The BRAF mutation leads to greatly increased activation of the signaling pathways for melanocyte growth, survival, and metastasis. Recent studies have shown that Vemurafenib (a potent inhibitor of mutated BRAF) had significant anti-tumor effects with improved survival and long-term outcomes in stage 3 and 4, V600E positive melanoma patients. This patients presence of BRAF mutation in the tissue most likely indicates a diagnosis of metastatic melanoma. (Choice A) Glioblastoma has been associated with overexpression of growth factors (such as PDGF, EGFR, s IGF, and TGF), but has not been associated with the BRAF mutation. (Choice C) The presence of BRCA1 and BRCA2 increases the ri