Embed Size (px)
Citation preview
The origin of metastatic disease: clues from genomics
7/13/2011
Tumor evolution
Metastasis: Current questions
• When do tumor cells leave the primary tumor?
• Are metastases clonal?• Do metastases evolve at
the metastatic site?• Do different tumor
types have different metastatic origins?
Nguyen, D. J Pathol 2011; 223:195-204
Why do we care?
• Treatment for metastasis is virtually non-existent• Some treatments increase the likelihood of
metastasis• Analyzing the primary tumor may indicate the
genetic make-up of metastases • Diagnostics do not exist for metastases, but may be
required if metastases are genetically dissimilar to the primary tumor
• CSCs might be a source of metastasis that are refractory to current treatment
Genomic studies of metastases
• How do we track the differences between primary tumors and mets?
• Loss of heterozygosity: two distinct alleles exist in normal tissue, one is lost in tumor
• Copy number: number of alleles or chromosomes increases or decreases
• Epigenetic markers: methylation states
Loss of heterozygosity
• Caused by– Non-disjunction– Recombination– Double strand break
repair– Deletion
• Detect with SNPs or microsatelllites
Copy Number
• Measure of genomic instability• Detected by sequencing (single cell) or CGH
(tissue)
CGH
• Comparative Genomic Hybridization
• Label tumor vs. normal tissue
Metastasis: Current questions
• When do tumor cells leave the primary tumor?
• Are metastases clonal?• Do metastases evolve at
the metastatic site?• Do different tumor
types have different metastatic origins?
Nguyen, D. J Pathol 2011; 223:195-204
Metastasis: Current questions• When do tumor cells disseminate?
– Early: DTCs or Mets have fewer or different mutations than the primary tumor
– Late: DTCs or Mets look like aggressive primary tumor• Are metastases clonal?
– The entire met or all mets in the body look the same• Do metastases evolve at the metastatic site?
– No: Mets look like primary tumor– Yes: Mets show significant divergence from the primary tumor
• Do different tumor types have different metastatic origins?– Mets look like primary tumor in some cancers– Mets look different than primary tumor in other cancers
When do tumor cells disseminate?
Disseminated tumor cells
Metastasis
Primary tumor
DTCs often do not cluster with metastases or primary tumors
Conclusions and Caveats
• DTCs exist very early in tumor progression• Cytokeratin marker causes bias
Are Metastases Clonal?
Copy Number Analysis
Liu et al. Nature Medicine 15, 559 - 565 (2009)
Metastases are clonal in prostate cancer
• Metastases found in different regions of the body are clonal, implying a single cell of origin
Liu et al. Nature Medicine 15, 559 - 565 (2009)
Metastases are not clonal in breast cancer
Wu et al. Clin Cancer Res April 1, 2008 14; 1938
Primary tumors are similar to metastases
Copy number analysis of single cells
6% coverage
Navin et al. Nature 472, 90–94 (07 April 2011)
Copy number analysis of single cells in breast tumors
Stromal cells
Tumor cells
Navin et al. Nature 472, 90–94 (07 April 2011)
Navin et al. Nature 472, 90–94 (07 April 2011)
Copy number analysis of single cells
Clinical examples of tracing metastatic origin
• Breast cancer– Her2-pos– 65 PTs with 42 macrometastases and 18
micrometastases– In HER-2-positive PTs, 26 of 29 metastases were
HER-2-positive– HER-2 amplification and ER and PR status were
conserved in mets in 71% of cases
Strein et al. Pathol Res Pract. 2010 Apr 15;206(4):253-8
Similarities between primary tumor and metastases in colorectal cancer
Jones et al. PNAS March 18, 2008 vol. 105 no. 11 4283-4288
• Screened 233 known mutations in PTs and Mets
• Only seven not found in both
Jones et al. PNAS March 18, 2008 vol. 105 no. 11 4283-4288
Implications of this data
• Mets arise late from aggressive, advanced carcinoma cells
• Implies that genes required for primary tumor growth might confer metastatic ability
Primary tumors are significantly different than metastases
Clinical examples of tracing metastatic origin
Fehm et al. Breast Cancer Research 2009 11:R59
Clinical examples of tracing metastatic origin
Fehm et al. Breast Cancer Research 2009 11:R59
Significant divergence of Mets from PTs in breast cancer
Ramaswamy et al. Nature Genetics 33, 49 - 54 (2002)
Methylation states change between primary tumor and metastases in prostate cancer
Prostate cancer cell linesYegnasubramanian et al. Cancer Res March 15, 2004 64; 1975
Methylation states change between primary tumor and metastases
Yegnasubramanian et al. Cancer Res March 15, 2004 64; 1975
Methylation states change between primary tumor and metastases
Yegnasubramanian et al. Cancer Res March 15, 2004 64; 1975
Hypermethylation occurs in breast cancer metastases
Mehrotra et al. Clin Cancer Res. Vol. 10, 3104-3109, 2004.
Interpretations of this data
• Metastases require additional mutations to successfully grow at a distant site
• Three possible scenarios:– Metastatic cells leave the primary tumor early on– Metastatic cells leave the primary tumor late but
then require additional mutations to colonize a distant organ
– Clones exist in primary tumor but are not detected
The best current example of using genomics to understand metastatic origin
Metastases occur late in pancreatic cancer
Yachida et al. Nature 467, 1114–1117 (28 October 2010)
Yachida et al. Nature 467, 1114–1117 (28 October 2010)
Conclusions
• Some metastases are genetically similar to the primary tumor, while others are not
• Metastases can be clonal or heterogeneous• Information from primary tumor could help to determine
characteristics about metastases• Primary tumor diagnostics may not be sufficient• Origin of metastatic precursor may be early or late in tumor
progression• These studies imply that it may not be cancer-type
dependent• Studies are limited…
Stoecklein, N. H. and Klein, C. A. (2010). International Journal of Cancer, 126: 589–598.
Conclusions
Seems to be mostly patient or study dependent!
Future directions
• Next generation sequencing– Can get more accurate data– Single cell resolution
• Analysis of CTCs and DTCs• “Personalized medicine”
