A defined piece of single-stranded nucleic acid which is used to identify specific complementary-sequence nucleic acid molecules in an assay intended to be used to evaluate a clinical specimen to diagnose, monitor or predict genetic mutations (e.g., duplication) of the her2/neu/erbB2 [v-erb-B2 avian erythroblastic leukaemia viral oncogene homolog 2] gene, associated with solid malignant neoplasms (e.g., breast cancer, ovarian cancer, stomach cancer, carcinoma of the salivary glands).