Cell-free detection of methylated tumour DNA
Provided herein is a method for detecting a tumour that can be applied to cell-free samples, e.g., to cell-free detect circulating tumour DNA. The method utilizes detection of adjacent methylation signals within a single sequencing read as the basic positive tumour signal, thereby decreasing false positives. The method comprises extracting DNA from a cell-free sample obtained from a subject, bisulphite converting the DNA, amplifying regions methylated in cancer (e.g., CpG islands, CpG shores, and/or CpG shelves), generating sequencing reads, and detecting tumour signals. To increase sensitivity, biased primers designed based on bisulphite converted methylated sequences can be used. Target methylated regions can be selected from a pre-validated set according to the specific aim of the test. Absolute number, proportion, and/or distribution of tumour signals may be used for tumour detection or classification. The method is also useful in, e.g., predicting, prognosticating, and/or monitoring response to treatment, tumour load, relapse, cancer development, or risk.
1. A method of detecting the presence of uveal cancer, comprising:
amplifying multiple regions of tumour DNA extracted from a cell-free sample obtained from a human subject with a plurality of PCR primer pairs;
wherein the multiple regions are either
(a) the regions amplified by primer pairs as set forth in SEQ ID NOs: 977-978 and 979-980, or
(b) the regions amplified by primer pairs as set forth in SEQ ID NOs: 973-1008;
wherein individual primer pairs of the plurality of PCR primer pairs are modified to include non-native DNA sequences corresponding to methylation specific versions of the multiple regions by selecting C residues to be replaced with T residues according to their methylation status within individual regions of the multiple selected regions;
generating sequencing reads from the amplified regions;
aligning the sequencing reads with a reference sequence for each region with a computer, wherein the reference sequence is obtained from a sample obtained from a healthy human subject; and
detecting signals by using the computer to determine methylation status of CpG residues in each of the two or more selected regions;
wherein the presence of uveal cancer in the subject is indicated when a level of methylation of CpG residues within the two or more selected regions is greater than a level of methylation of CpG residues within the two or more selected regions for subjects without uveal cancer.
2. The method of claim 1 , further comprising determining sites of hydroxymethylation.
3. The method of claim 2 , wherein:
amplifying is carried out with at least one primer set designed to amplify at least one methylation site having a methylation value at or below −0.1, −0.2, −0.3, −0.4, or −0.5 in normal tissue; or
amplifying is carried out with at least one primer set designed to amplify at least one methylation site having a difference between the average methylation value in the cancer and the normal tissue of greater than 0.1, 0.2, 0.3, 0.4, or 0.5; or
amplifying is carried out with at least one primer set comprising primer pairs amplifying at least one methylation site having at least one adjacent methylation site within 200 base pairs that also has:
a methylation value at or below −0.1, −0.2, −0.3, −0.4, or −0.5 in normal tissue, and
a difference between the average methylation value in the cancer and the normal tissue of greater than 0.1, 0.2, 0.3, 0.4, or 0.5.
4. The method of claim 1 , wherein the detection of at least one signal is indicative of the presence of uveal cancer during one or more of:
determining response to treatment;
monitoring tumour load;
detecting residual tumour post-surgery;
detecting relapse;
performing a secondary screening;
performing a primary screening;
monitoring cancer development; and
monitoring cancer risk.
5. The method of claim 1 , further comprising either
(i) determining a distribution of signals across the multiple regions; and
comparing the distribution to at least one pattern associated with uveal cancer;
wherein similarity between the distribution and the pattern is indicative of uveal cancer; or
(ii) comparing the distribution to a plurality of patterns, each one associated with uveal cancer;
wherein similarity between the distribution and one of the plurality of patterns is indicative of the uveal cancer.
6. A kit for detecting the presence of uveal cancer in tumour DNA extracted from a cell-free sample obtained from a human subject, the kit comprising:
reagents for carrying out a method of detecting uveal cancer, the reagents comprising either
(a) primer pairs as set forth in SEQ ID NOs: 977-978 and 979-980, or
(b) primer pairs as set forth in SEQ ID NOs: 973-1008.
7. A method of detecting the presence of uveal cancer and treating uveal cancer, comprising:
amplifying multiple regions of tumour DNA extracted from a cell-free sample obtained from a human subject, with a plurality of PCR primer pairs;
wherein the multiple regions are either
(a) the regions amplified by primer pairs as set forth in SEQ ID NOs: 977-978 and 979-980, or
(b) the regions amplified by primer pairs as set forth in SEQ ID NOs: 973-1008;
wherein individual primer pairs of the plurality of PCR primer pairs are modified to include non-native DNA sequences corresponding to methylation specific versions of the multiple regions by selecting C residues to be replaced with T residues according to their methylation status within individual regions of the multiple selected regions;
generating sequencing reads from the amplified regions;
aligning the sequencing reads with a reference sequence for each region with a computer, wherein the reference sequence is obtained from a sample obtained from a healthy human subject; and
detecting signals by using the computer to determine methylation status of CpG residues in each of the two or more selected regions;
determining that a level of methylation within the two or more selected regions is greater than a level of methylation within the two or more selected regions in subjects without uveal cancer which is indicative of the human subject having uveal cancer; and
administering an anti-uveal cancer treatment to the human subject determined to have uveal cancer.
8. A method of detecting the presence of uveal cancer, comprising:
amplifying multiple regions of tumour DNA extracted from a cell-free sample obtained from a human subject, with either
(a) primer pairs as set forth in SEQ ID NOs: 977-978 and 979-980, or
(b) primer pairs as set forth in SEQ ID NOs: 973-1008;
wherein individual primer pairs of the plurality of PCR primer pairs are modified to include non-native DNA sequences corresponding to methylation specific versions of the multiple regions by selecting C residues to be replaced with T residues according to their methylation status within individual regions of the multiple selected regions;
generating sequencing reads from the amplified regions;
aligning a computer to align the sequencing reads with a reference sequence for each region with a computer, wherein the reference sequence is obtained from a sample obtained from a healthy human subject; and
detecting signals by using the computer to determine methylation status of CpG residues in each of the two or more selected regions;
wherein the presence of uveal cancer in the subject is indicated when a level of methylation of CpG residues within the two or more selected regions is greater than a level of methylation of CpG residues within the two or more selected regions for subjects without uveal cancer.
9. A method, comprising:
amplifying multiple regions of tumour DNA extracted from a cell-free sample obtained from a human subject with a plurality of PCR primer pairs;
wherein the multiple regions are either
(a) the regions amplified by primer pairs as set forth in SEQ ID NOs: 977-978 and 979-980, or
(b) the regions amplified by primer pairs as set forth in SEQ ID NOs: 973-1008;
wherein individual primer pairs of the plurality of PCR primer pairs are modified to include non-native DNA sequences corresponding to methylation specific versions of the multiple regions by selecting C residues to be replaced with T residues according to their methylation status within individual regions of the multiple selected regions;
generating sequencing reads from the amplified regions;
aligning the sequencing reads with a reference sequence for each region with a computer, wherein the reference sequence is obtained from a sample obtained from a healthy human subject; and
detecting signals by using the computer to determine methylation status of CpG residues in each of the two or more selected regions.