Detection of genetic or molecular aberrations associated with cancer
Biological samples including cell-free DNA fragments are analyzed to identify imbalances in chromosomal regions, e.g., due to deletions and/or amplifications in a tumor. Multiple loci are used for each chromosomal region. Such imbalances can then be used to diagnose (screen) a patient for cancer, as well as prognosticate a patient with cancer, or to detect the presence or to monitor the progress of a premalignant condition in a patient. The severity of an imbalance as well as the number of regions exhibiting an imbalance can be used. A systematic analysis of non-overlapping segments of a genome can provide a general screening tool for a sample. Additionally, a patient can be tested over time to track severity of each of one or more chromosomal regions and a number of chromosomal regions to enable screening and prognosticating, as well as monitoring of progress (e.g. after treatment).
1. A method of analyzing a biological sample of an organism for chromosomal deletions or amplifications associated with cancer, the biological sample including nucleic acid molecules originating from normal cells and potentially from cells associated with cancer, wherein at least some of the nucleic acid molecules are cell-free in the biological sample, the method comprising:
determining first and second haplotypes for normal cells of the organism at a first chromosomal region, the first chromosomal region including a first plurality of loci, wherein the first and second haplotypes are heterozygous at each of the first plurality of loci;
for each of a plurality of the nucleic acid molecules in the biological sample:
identifying a location of the nucleic acid molecule in a reference genome of the organism; and
determining a respective allele of the nucleic acid molecule;
identifying a first group of nucleic acid molecules as being from the first haplotype based on the identified locations and determined alleles, the first group including at least one nucleic acid molecule located at each of the first plurality of loci;
identifying a second group of nucleic acid molecules as being from the second haplotype based on the identified locations and determined alleles, the second group including at least one nucleic acid molecule located at each of the first plurality of loci;
calculating, with a computer system, a first value of the first group of nucleic acid molecules, the first value defining a property of the nucleic acid molecules of the first group;
calculating, with the computer system, a second value of the second group of nucleic acid molecules, the second value defining a property of the nucleic acid molecules of the second group; and
comparing the first value to the second value to determine a classification of
whether the first chromosomal region exhibits a deletion or an amplification in any cells associated with cancer, wherein the comparison includes determining a difference or a ratio between the first value and the second value, and wherein the classification includes comparing the difference or the ratio to at least one threshold value.
2. The method of claim 1 , wherein the first chromosomal region is classified as exhibiting a deletion or an amplification in cells associated with cancer, and wherein the cells associated with cancer include a malignant tumor and/or from a premalignant lesion.
3. The method of claim 1 , wherein each locus of the first plurality of loci is at least 500 bases apart from another locus of the first plurality of loci.
4. The method of claim 1 , wherein the at least one threshold value is derived from a healthy organism or from a region not having a deletion or amplification, wherein the sequential probability ratio testing, the t-test, or the chi-square test is used to determine the at least one threshold value.
5. The method of claim 1 , wherein the first value corresponds to a statistical value of a size distribution of the nucleic acid molecules of the first group, and the second value corresponds to a statistical value of a size distribution of the nucleic acid molecules of the second group.
6. The method of claim 5 , wherein the first value is an average size of the nucleic acid molecules of the first group, and the second value is an average size of the nucleic acid molecules of the second group.
7. The method of claim 5 , wherein the first value Q HapI is a fraction of nucleic acid molecules in the first group that are shorter than a cutoff size, and the second value Q HapII is a fraction of nucleic acid molecules in the second group that are shorter than the cutoff size.
8. The method of claim 7 , wherein the comparison includes determining the difference between the first value and the second value, wherein the difference is ΔQ=Q HapI−Q HapII , and wherein a positive value of ΔQ greater than a threshold value indicates that the second haplotype includes a deletion in tumor tissue in the organism or that the first haplotype includes an amplification in tumor tissue in the organism.
9. The method of claim 7 , wherein the comparison includes determining the difference between the first value and the second value, wherein the difference is ΔQ=Q HapI −Q HapII , and wherein an approximate value of zero for ΔQ indicates that no deletion or amplification exists in the first chromosomal region.
10. The method of claim 5 , wherein the first value F HapI and the second value F HapII are defined for a respective haplotype as F=Σ w length/Σ N length, where Σ w length represents a sum of lengths of the nucleic acid molecules of the corresponding group with a length equal to or less than a cutoff size w; and Σ N length represents a sum of lengths of the nucleic acid molecules of the corresponding group with a length equal to or less than N bases, where N is greater than w.
11. The method of claim 10 , wherein the comparison includes determining the difference between the first value and the second value, and wherein the difference is ΔF=F Hap I −F Hap II , and wherein a positive value of ΔF greater than a threshold value indicates that the second haplotype includes a deletion in tumor tissue in the organism.
12. The method of claim 10 , wherein the comparison includes determining the difference between the first value and the second value, and wherein the difference is ΔF=F Hap I −F Hap II , and wherein a negative value of ΔF greater than a threshold value indicates that the second haplotype includes an amplification in tumor tissue in the organism.
13. The method of claim 1 , wherein the first value of the first group corresponds to a number of nucleic acid molecules located at the first plurality of loci, and the second value of the second group corresponds to a number of nucleic acid molecules located at the first plurality of loci.
14. The method of claim 13 , further comprising:
calculating the ratio of the first value and the second value to determine a fractional concentration of cancer DNA in the biological sample.
15. The method of claim 14 , further comprising:
determining the fractional concentration of cancer DNA in the biological sample at a plurality of times; and
using the fractional concentration at the plurality of times to diagnose, stage, prognosticate, or monitor progress of a level of cancer in the organism.
16. The method of claim 1 , further comprising:
for each of a plurality of other chromosomal regions:
repeating the method of claim 1 ;
determining a first number of chromosomal regions that exhibit a deletion or an amplification; and
comparing the first number to one or more threshold values to determine a level of cancer in the organism.
17. The method of claim 16 , further comprising:
determining an amount of deletion or amplification for each chromosomal region that was identified as exhibiting a deletion or an amplification; and
comparing the amount to one or more threshold values to determine the level of cancer in the organism.
18. The method of claim 16 , further comprising:
repeating the method of claim 16 at a plurality of times; and
using the first number at the plurality of times to diagnose, stage, prognosticate, or monitor progress of the level of cancer in the organism.
19. The method of claim 18 , wherein using the first number at the plurality of times to diagnose, stage, prognosticate, or monitor progress of the level of cancer in the organism includes determining the presence or progress of a premalignant condition.
20. The method of claim 16 , wherein each of the chromosomal regions are of predetermined length.
21. A computer program product comprising a computer readable medium storing a plurality of instructions for controlling a processor to perform an operation for analyzing a biological sample of an organism for chromosomal deletions or amplifications associated with cancer, the operation comprising:
determining first and second haplotypes for normal cells of the organism at a first chromosomal region, the first chromosomal region including a first plurality of loci, wherein the first and second haplotypes are heterozygous at each of the first plurality of loci;
for each of a plurality of the nucleic acid molecules in the biological sample:
identifying a location of the nucleic acid molecule in a reference genome of the organism; and
determining a respective allele of the nucleic acid molecule;
identifying a first group of nucleic acid molecules as being from the first haplotype based on the identified locations and determined alleles, the first group including at least one nucleic acid molecule located at each of the first plurality of loci;
identifying a second group of nucleic acid molecules as being from the second haplotype based on the identified locations and determined alleles, the second group including at least one nucleic acid molecule located at each of the first plurality of loci;
calculating a first value of the first group of nucleic acid molecules, the first value defining a property of the nucleic acid molecules of the first group;
calculating a second value of the second group of nucleic acid molecules, the second value defining a property of the nucleic acid molecules of the second group; and
comparing the first value to the second value to determine a classification of
whether the first chromosomal region exhibits a deletion or an amplification in any cells associated with cancer, wherein the comparison includes determining a difference or a ratio between the first value and the second value, and wherein the classification includes comparing the difference or the ratio to at least one threshold value.
22. A computer system for analyzing a biological sample of an organism for chromosomal deletions or amplifications associated with cancer, the computer system comprising:
one or more processors configured to implement the method of claim 1 .
23. The computer program product of claim 21 , wherein the first chromosomal region is classified as exhibiting a deletion or an amplification in cells associated with cancer, and wherein the cells associated with cancer include a malignant tumor and/or from a premalignant lesion.
24. The computer program product of claim 21 , wherein each locus of the first plurality of loci is at least 500 bases apart from another locus of the first plurality of loci.
25. The computer program product of claim 21 , wherein the at least one threshold value is derived from a healthy organism or from a region not having a deletion or amplification, wherein the sequential probability ratio testing, the t-test, or the chi-square test is used to determine the at least one threshold value.
26. The computer program product of claim 21 , wherein the first value corresponds to a statistical value of a size distribution of the nucleic acid molecules of the first group, and the second value corresponds to a statistical value of a size distribution of the nucleic acid molecules of the second group.
27. The computer program product of claim 26 , wherein the first value is an average size of the nucleic acid molecules of the first group, and the second value is an average size of the nucleic acid molecules of the second group.
28. The computer program product of claim 26 , wherein the first value Q HapI is a fraction of nucleic acid molecules in the first group that are shorter than a cutoff size, and the second value Q HapII is a fraction of nucleic acid molecules in the second group that are shorter than the cutoff size.
29. The computer program product of claim 28 , wherein the comparison includes determining the difference between the first value and the second value, wherein the difference is ΔQ=Q HapI −Q HapII , and wherein a positive value of ΔQ greater than a threshold value indicates that the second haplotype includes a deletion in tumor tissue in the organism or that the first haplotype includes an amplification in tumor tissue in the organism.
30. The computer program product of claim 28 , wherein the comparison includes determining the difference between the first value and the second value, wherein the difference is ΔQ=Q HapI −Q HapII , and wherein an approximate value of zero for ΔQ indicates that no deletion or amplification exists in the first chromosomal region.
31. The computer program product of claim 26 , wherein the first value F Hap I and the second value F Hap II are defined for a respective haplotype as F=Σ w length/Σ N length, where Σ w length represents a sum of lengths of the nucleic acid molecules of the corresponding group with a length equal to or less than a cutoff size w; and Σ N length represents a sum of lengths of the nucleic acid molecules of the corresponding group with a length equal to or less than N bases, where N is greater than w.
32. The computer program product of claim 31 , wherein the comparison includes determining the difference between the first value and the second value, and wherein the difference is ΔF=F Hap I −F Hap II , and wherein a positive value of ΔF greater than a threshold value indicates that the second haplotype includes a deletion in tumor tissue in the organism.
33. The computer program product of claim 31 , wherein the comparison includes determining the difference between the first value and the second value, and wherein the difference is ΔF=F Hap I −F Hap II , and wherein a negative value of ΔF greater than a threshold value indicates that the second haplotype includes an amplification in tumor tissue in the organism.
34. The computer program product of claim 21 , wherein the first value of the first group corresponds to a number of nucleic acid molecules located at the first plurality of loci, and the second value of the second group corresponds to a number of nucleic acid molecules located at the first plurality of loci.
35. The computer program product of claim 34 , wherein the operation further comprises:
calculating the ratio of the first value and the second value to determine a fractional concentration of cancer DNA in the biological sample.
36. The computer program product of claim 35 , wherein the operation further comprises:
determining the fractional concentration of cancer DNA in the biological sample at a plurality of times; and
using the fractional concentration at the plurality of times to diagnose, stage, prognosticate, or monitor progress of a level of cancer in the organism.
37. The computer program product of claim 21 , wherein the operation further comprises:
for each of a plurality of other chromosomal regions:
determining a classification of whether the other chromosomal region exhibits a deletion or an amplification;
determining a first number of chromosomal regions that exhibit a deletion or an amplification; and
comparing the first number to one or more threshold values to determine a level of cancer in the organism.
38. The computer program product of claim 37 , wherein the operation further comprises:
determining an amount of deletion or amplification for each chromosomal region that was identified as exhibiting a deletion or an amplification; and
comparing the amount to one or more threshold values to determine the level of cancer in the organism.
39. The computer program product of claim 37 , wherein the operation further comprises:
determining the first number of chromosomal regions that exhibit a deletion or an amplification at a plurality of times; and
using the first number at the plurality of times to diagnose, stage, prognosticate, or monitor progress of the level of cancer in the organism.
40. The computer program product of claim 39 , wherein using the first number at the plurality of times to diagnose, stage, prognosticate, or monitor progress of the level of cancer in the organism includes determining the presence or progress of a premalignant condition.
41. The computer program product of claim 37 , wherein each of the chromosomal regions are of predetermined length.