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Presence of fetal DNA in maternal plasma and serum

1described the presence of cell-free nucleic acid (cfNA) in human blood for the first time. This attracted little attention in the scientific community and it was not until 1994 that the importance of cfNA was recognized as a result of the detection of mutated RAS gene fragments in the blood of cancer patients 2,3 (TIMELINE). In 1996, microsatellite alterations on cell-free DNA (cfDNA) were shown in cancer patients 4

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Cell-free nucleic acids as biomarkers in cancer patients

Increased levels of DNA fragments have frequently been found in the blood plasma of cancer patients. Published data suggest that only a fraction of the DNA in blood plasma is derived from cancer cells. However, it is not known how much of the circulating DNA is from cancer or from noncancer cells. By quantitative methylation-specific PCR of the promoter region of the CDKN2A tumor suppressor gene, we were able to quantify the fraction of plasma DNA derived from tumor cells. In the plasma samples of 30 unselected cancer patients, we detected quantities of tumor DNA from only 3% to as much as 93% of total circulating DNA. We investigated possible origins of nontumor DNA in the plasma and demonstrate here a contribution of T-cell DNA in a few cases only. To investigate the possibility that plasma DNA originates from apoptotic or necrotic cells, we performed studies with apoptotic (staurosporine) and necrotic (staurosporine plus oligomycin) cells in vitro and with mice after induction of apoptotic (anti-CD95) or necrotic (acetaminophen) liver injury. Increasing amounts of DNA were found to be released in the supernatants of cells and in the blood plasma samples of treated animals. A clear discrimination of apoptotic and necrotic plasma DNA was possible by gel electrophoresis. The same characteristic patterns of DNA fragments could be identified in plasma derived from different cancer patients. The data are consistent with the possibility that apoptotic and necrotic cells are a major source for plasma DNA in cancer patients.

https://cancerres.aacrjournals.org/content/canres/61/4/1659.full.pdf

DNA Fragments in the Blood Plasma of Cancer Patients: Quantitations and Evidence for Their Origin from Apoptotic and Necrotic Cells

From the Departments of Thoracic/Head and Neck Medical Oncology (R.S.H., J.V.H., S.M.L.), Cancer Biology (R.S.H., J.V.H.), and Clinical Cancer Prevention (S.M.L.), University of Texas M.D. Anderson Cancer Center, Houston. Address reprint requests to Dr. Lippman at the Department of Thoracic/Head and Neck Medical Oncology, Unit 432, M.D. Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030, or at slippman@ mdanderson.org.

Molecular origins of cancer: Lung cancer

Background The management of metastatic breast cancer requires monitoring of the tumor burden to determine the response to treatment, and improved biomarkers are needed. Biomarkers such as cancer antigen 15-3 (CA 15-3) and circulating tumor cells have been widely studied. However, circulating cell-free DNA carrying tumor-specific alterations (circulating tumor DNA) has not been extensively investigated or compared with other circulating biomarkers in breast cancer. Methods We compared the radiographic imaging of tumors with the assay of circulating tumor DNA, CA 15-3, and circulating tumor cells in 30 women with metastatic breast cancer who were receiving systemic therapy. We used targeted or whole-genome sequencing to identify somatic genomic alterations and designed personalized assays to quantify circulating tumor DNA in serially collected plasma specimens. CA 15-3 levels and numbers of circulating tumor cells were measured at identical time points. Results Circulating tumor DNA was successfully detected in 29 of the 30 women (97%) in whom somatic genomic alterations were identified; CA 15-3 and circulating tumor cells were detected in 21 of 27 women (78%) and 26 of 30 women (87%), respectively. Circulating tumor DNA levels showed a greater dynamic range, and greater correlation with changes in tumor burden, than did CA 15-3 or circulating tumor cells. Among the measures tested, circulating tumor DNA provided the earliest measure of treatment response in 10 of 19 women (53%). Conclusions This proof-of-concept analysis showed that circulating tumor DNA is an informative, inherently specific, and highly sensitive biomarker of metastatic breast cancer. (Funded by Cancer Research UK and others.)

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Analysis of Circulating Tumor DNA to Monitor Metastatic Breast Cancer

Microsatellite instability is an important characteristic of many tumor types1–8 especially those associated with hereditary non–polyposis colorectal carcinoma (HNPCC) syndrome6–8. Microsatellite alterations in 50% of primary small cell lung carcinoma (SCLC) have been found. These alterations were also found in the sputum4. Because neoplastic characteristics such as decreased strand stability9 and ras mutations10–12 have been found in the plasma DNA of cancer patients, we looked for microsatellite alterations in the plasma of SCLC patients. A microsatellite alteration was present in 16 out of 21 (76%) SCLC tumors and in 15 out of 21 (71%) plasma samples. In one case, the alteration was present only in the plasma DNA. If confirmed in larger studies, microsatellite analysis of plasma DNA might constitute a new tool for tumor staging, management and, possibly, detection.

Microsatellite alterations in plasma DNA of small cell lung cancer patients.

Small amounts of free DNA circulate in both healthy and diseased human plasma/serum, and increased concentrations of DNA are present in the plasma of cancer patients. Characteristics of tumour DNA have been found in genetic material extracted from the plasma of cancer patients. These features include decreased strand stability and the presence of specific oncogene, tumour suppressor gene and microsatellite alterations. Point mutations of the ras genes have been detected in the plasma DNA of patients suffering from haematopoetic malignancies, colorectal and pancreatic cancer, sometimes prior to clinical diagnosis. Rearranged immunoglobulin heavy chain DNA has been found in the plasma of patients with non-Hodgkins lymphoma and acute B cell leukaemia. Microsatellite instability, expressed either as a new allele or a loss of one allele (LOH) occurs in the plasma and serum DNA of patients suffering from head and neck, lung and renal cell cancer. The results obtained in many different cancers have opened a new research area indicating that plasma DNA might eventually be a suitable target for the development of non-invasive diagnostic, prognostic and follow-up tests for cancer.

Detection of circulating tumour DNA in the blood (plasma/serum) of cancer patients.

Although it is evident that DNA circulates freely in blood plasma both in disease and in health, the source of this DNA remains enigmatic. It can be presumed that circulating DNA in healthy subjects derives from lymphocytes or other nucleated cells. Yet, it is not known why cancer patients have such large quantities of plasma DNA. There is no doubt that a proportion seems to originate from nucleated blood cells since wild-type DNA has been detected in the plasma of all cancer patients studied as well as in that of healthy controls. However, a substantial proportion of plasma DNA in cancer patients derives from tumor cells. This latter concept is supported by both quantitative and qualitative observations. Plasma DNA levels are not only greater in cancer patients than in normal subjects,1–5 but also correlate inversely with outcome and tend to fall with effective treatment.1,5 In addition, the ability to detect LOH in plasma DNA6–13 suggests that tumor-related DNA is the predominant subtype in at least some cancer patients. What is responsible for the presence of tumor DNA shed in the bloodstream? It could be due to lysis of circulating cancer cells or of micrometastases, to DNA leakage resulting from tumor necrosis or apoptosis, or to a new mechanism of active release.

The origin and mechanism of circulating DNA.

K-ras mutations are found in DNA extracted from the plasma of patients with colorectal cancer

Tumor-derived circulating DNA has been found in the plasma of cancer patients. Alterations include decreased strand stability, mutations of oncogenes or of tumor suppressor genes, microsatellite alterations, and hypermethylation of several genes. RNA has also been found circulating in the plasma of normal subjects and cancer patients. Tyrosinase mRNA has been extracted from the serum of melanoma patients and subjected to RT-PCR. Moreover, the presence of cell-free EBV-associated RNA has been reported in the plasma of patients with nasopharyngeal carcinoma. Human telomerase comprises two RNA subunits, telomerase RNA template (hTR) and its catalytic component, telomerase reverse transcriptase protein (hTERT). Expression of these subunits correlates with telomerase activity. Using RT-PCR, we investigated whether these RNA subunits were present in the serum of 18 patients with breast cancer, 2 patients with benign breast disease, and 21 normal subjects. The presence of amplifiable RNA was confirmed in all tissue and serum samples using RT-PCR of glyceraldehyde-3-phosphate dehydrogenase RNA. hTR was found in 17 of 18 tumors (94%) and 5 of 18 serum samples (28%). hTERT was also detected in 17 of 18 tumors (94%) and in 4 of 16 available serum samples (25%). hTR and hTERT were undetectable in tissues and sera taken from 2 patients with benign disease and in the sera of 21 normal subjects. We conclude that RNA is detectable in the serum of breast cancer patients and that tumor-derived mRNA can be extracted and amplified using RT-PCR, even in patients with localized disease. This may have implications for cancer diagnosis and follow-up in the future.

https://clincancerres.aacrjournals.org/content/clincanres/6/10/3823.full.pdf

Xu Qi Chen

Papers

Microsatellite alterations in plasma DNA of small cell lung cancer patients.

Detection of circulating tumour DNA in the blood (plasma/serum) of cancer patients.

The origin and mechanism of circulating DNA.

K-ras mutations are found in DNA extracted from the plasma of patients with colorectal cancer

Telomerase RNA as a Detection Marker in the Serum of Breast Cancer Patients