Loss of heterozygosity in serial plasma DNA samples during follow‐up of women with breast cancer

Abstract

We evaluated the potential utility of occult circulating tumor DNA as a molecular marker of disease in subjects previously diagnosed with breast cancer. Using 24 microsatellite markers located at sites of frequent loss of heterozygosity (LOH) or allele imbalance in breast cancer, we analyzed DNA from 16 primary tumors (Stage IIA or more advanced) and 30 longitudinally collected plasma specimens. Clinical data at the time of plasma collection were obtained. All 16 tumors were characterized by an individual pattern of LOH. LOH was detected in 12 of 30 (40%) plasma samples, taken from 8 of 14 (57%) subjects. However, the number of LOH in plasma was small (n ‫؍‬ 15), and the mean proportion of LOH was much lower than in the tumors (0.05 vs. 0.52). Although infrequent, 12 of 15 (80%) plasma LOH were concordant with abnormalities in the paired tumors, and the mean percent LOH was higher than in normal plasmas, suggesting that they were authentic tumor-derived abnormalities. We found, despite this, no association, between plasma LOH and tumor stage or clinical status at time of blood collection (i.e., LOH was as common in subjects with no evident disease as in those with evident disease). In addition, detection of LOH was not consistent between serial samples from 5 of 11 subjects (45%), despite stable clinical conditions. No association with clinical outcome was evident, although the sample size was small. Microsatellite instability in plasma was infrequent, nonconcordant with paired tumor and inconsistent in serial samples. This pilot study suggests that identifying tumor-specific LOH in the plasma of breast cancer subjects may not be useful for detecting occult metastases or for monitoring disease. Other detection techniques may be more promising, but circulating tumor DNA may not be a sufficiently accurate reflection of breast cancer clinical status or tumor activity.

Quantitative Detection of p53 Mutations in Plasma DNA from Tobacco Smokers

“…The matched plasma from this sample was negative for p53 mutations using the mutation load assay. Several reports observed concordance between mutations in serum/plasma DNA and tumors (56)(57)(58)(59), whereas other reports noted inconsistency between matched samples (28,43,44,60). The lack of detection of codon 248 p53 mutation in the matched plasma DNA sample could be due to cycling of p53-mutated DNA or presence of p53-mutated DNA only a certain period after exposure.…”

Identification of Loss of Heterozygosity on Circulating Free DNA in Peripheral Blood of Prostate Cancer Patients: Potential and Technical Improvements

“…The observation that tumor-specific plasma DNA is largely diluted by normal DNA has been discussed for other tumor entities (19 -21 ). Furthermore, circulating plasma DNA was suggested not to accurately reflect the clinical status of breast tumor progression (34 ). Diehl et al (24 ) showed that the fraction of mutant APC (adenomatous polyposis coli) DNA fragments in plasma varied according to tumor stage of colorectal cancer patients, and the fraction of mutant APC fragments in plasma of patients with advanced tumors was 11% of the total APC fragments.…”

Quantitative Multiplex Methylation-Specific PCR Assay for the Detection of Promoter Hypermethylation in Multiple Genes in Breast Cancer

“…This has also been reported for FHIT (44), APC, and CDH1 (13). Wang et al (45) reported that nearly every breast tumor has an individual pattern of allelic imbalance or loss of heterozygosity at multiple loci, which constitutes its "fingerprint. "…”