Compositions and methods for detecting a mutant variant of a polynucleotide

A method of detecting a cancer cell and/or polynucleotide associated with cancer in a sample obtained from a subject, the method comprising

• (a) contacting a first polynucleotide strand of a double stranded polynucleotide with a first primer having a 3′ end region, wherein the 3′ end region comprises a portion complementary to a mutation positioned within a region of a polynucleotide, and a blocking oligonucleotide comprising a blocking moiety and having a 5′ end region, wherein the 5′ end region comprises a portion complementary to a wild-type sequence corresponding to the region comprising the mutation within the first polynucleotide strand, wherein the first primer and the blocking oligonucleotide compete for binding to the region of the first polynucleotide strand encompassing the mutation, and
• (b) contacting the second polynucleotide strand or the first polynucleotide strand of the double stranded polynucleotide with a second primer comprising a sequence substantially complementary to a sequence on the second strand of the polynucleotide or the first polynucleotide strand that is 5′ of the region corresponding to where the first primer binds the first polynucleotide strand;
• and
• (c) detecting an amplicon in the sample, wherein detection of an amplicon indicates the presence of a cancer cell and/or polynucleotide associated with cancer in the sample.