The present invention discloses a method of detecting a wild-type or mutant B-RAF gene in a body fluid sample from a subject. Also disclosed are methods of using B-RAF as a biomarker for detecting cancer, predicting the outcome of cancer, and monitoring the treatment of cancer or the status of cancer. Furthermore, the invention discloses methods and compositions for detecting a mutant gene with a peptide nucleic acid clamp capable of hybridizing to a wild-type gene and a locked nucleic acid probe capable of hybridizing to a mutant of the gene.
