Detection of mitochondrial DNA mutations in primary breast cancer and fine-needle aspirates

To determine the frequency and distribution of mitochondrial DNA mutations in breast cancer, 18 primary breast tumors were analyzed by direct sequenci ng. Twelve somatic mutations not present in matched lymphocytes and normal breast tissues were detected in 11 of the tumors screened (61%). Of these m utations, five (42%) were deletions or insertions in a homopolymeric C-stre tch between nucleotides 303-315 (D310) within the D-loop. The remaining sev en mutations (58%) were single-base substitutions in the coding (ND1, ND4, ND5, and cytochrome b genes) or noncoding regions (D-loop) of the mitochond rial genome. In three cases (25%), the mutations detected in coding regions led to amino acid substitutions in the protein sequence. We then screened an additional 46 primary breast tumors with a rapid PCR-based assay to iden tify poly-C alterations in D310, and we found seven more cancers with alter ations. Using D310 mutations as clonal marker, we detected identical change s in five of five matched fine-needle aspirates and in four of four metasta ses-positive lymph nodes. The high frequency of D310 alterations in primary breast cancer combined with the high sensitivity of the PCR-based assays p rovides a new molecular tool for cancer detection.