Highlights of This Issue

Although changes in mitochondrial DNA (mtDNA) copy number have been implicated in different cancers, specific data on mtDNA copy number and colorectal cancer risk have been lacking. To address this lack of data, Thyagarajan and colleagues evaluated the association between mtDNA copy number and colorectal cancer risk among participants in the Singapore Chinese Health Study. The authors report that Individuals with low and high relative mtDNA copy numbers both showed increased risk of colorectal cancer, suggesting that mtDNA may play a critical role in colorectal cancer development.

BRCA1/2 mutation carriers are recommended to undergo breast cancer screening with magnetic resonance imaging (MRI) because of the high sensitivity of MRI. To evaluate the impact of various screening protocols on cancer detection and mortality, Heijnsdijk and colleagues analyzed 3 studies of BRCA1/2 mutation carriers who were undergoing the recommended annual MRI and mammography screenings. The model from this analysis predicts breast cancer mortality reductions of 42% to 47% for mammography screening, 48% to 61% for MRI screening, and 50% to 62% for combined screening. These studies suggest substantial mortality benefits with the use of MRI to screen BRCA1/2 mutation carriers.

To test cell-cycle proteins as predictive markers in urothelial carcinoma, Lenz and colleagues assembled tissue from 491 bladder cancer cases as tissue microarrays and examined them for aberrant expression of p53, p63, p16, cyclin D1, Rb, and Ki-67. The authors report that overexpression of p53 and Ki-67 was associated with high-grade tumors, whereas expression of p63 and p16 was decreased in high-grade tumors. These results reveal significant heterogeneity in the expression of key cell-cycle proteins in bladder cancer tissue.

To identify novel gene variants for breast cancer risk, Higginbotham and colleagues conducted a multistage genetic association study in a series of breast cancer study populations. In their analysis, over 1,100 single-nucleotide polymorphisms were examined for evidence of association with breast cancer in independent study groups. The authors found that a series of validated breast cancer risk variants yielded the expected associations. In addition, 2 previously unreported loci were significantly associated with breast cancer risk in 3 of the 4 study populations. This important report adds to the compendium of known breast cancer genetic risk variants.