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Clinicopathologic significance of DNA mismatch repair defects in endometrial cancer: The devil is in the details
Gynecologic Oncology 113 (2009) 151–152
Contents lists available at ScienceDirect
Gynecologic Oncology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / y g y n o
Editorial
Clinicopathologic significance of DNA mismatch repair defects in endometrial cancer: The devil is in the details Loss of genome stability is a feature of cancer cells [1,2]. The molecular and clinical progression of tumors depends on failures in normal DNA repair processes. The notion that tumor cells are hypermutable (have a so-called mutator phenotype) was first put forth by Loeb in 1991 [3] and loss of DNA mismatch repair (DMMR) was first described in human tumors in 1993 [4-7]. Naturally occurring strand slippage mutations in short repetitive elements go unrecognized in tumor cells that lack DMMR. The consequence is the accumulation of insertion and deletion mutations that are products of replication errors. Tumors with these sorts of abnormalities in repetitive DNA sequences have been referred to as RER-positive (replication error-positive). The DNA sequences most subject to strand slippage mutations are called microsatellites, and consequently the tumor abnormality that is detected is also referred to as microsatellite instability (MSI). Tumor cells lacking DNA mismatch repair accumulate mutations at a much higher rate than those with an intact mismatch repair system. Endometrial cancers frequently have defects in DNA mismatch repair with ∼25% of all endometrial cancers exhibiting the tumor DNA MSI-positive phenotype. The remaining 75% of tumors are referred to as microsatellite stable (MSS). Arabi and colleagues report the results of a study in which they assessed DNA mismatch repair status in high-grade endometrial cancers. Their analysis of 91 cases suggests that loss of DNA mismatch repair may be associated with adverse outcomes. This is an interesting finding, with clear clinical implications. It is also somewhat unexpected. Previous work had suggested that loss of DNA mismatch repair is associated with poor outcomes [8], improved outcomes [9,10], or similar outcomes relative to MSS cases [11]. It is important to consider the similarities and differences between the studies that have been reported to date, particularly the molecular approaches to measuring defects in DNA mismatch repair and the patient populations being investigated. There are several explanations for why studies might differ with respect to their conclusions regarding the clinical significance of loss of DNA mismatch repair. The underlying heterogeneity of patient populations is likely to explain some of the differences. Work by Arabi and colleagues presented in this issue of Gynecologic Oncology is a single-institution study for which efforts were made to capture all patients of interest. One caveat, however, is that only high-grade endometrial carcinomas were studied. The authors evaluated both type I (endometrioid) and type II (non-endometrioid) cancers. Other studies have been based on relatively small series or surveying loss of mismatch repair in different histologic types, while others have studied all histologic subtypes of uterine cancer and still others have focused on endometrioid cancers only [8,10-13]. The methods used to assess loss of DNA mismatch repair could also explain some of the variability in the results reported to date. As 0090-8258/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.ygyno.2009.03.013
noted, loss of DNA mismatch repair results in accumulation of mutations in microsatellite sequences leading to MSI-positive tumors. The underlying molecular defect is the loss of function of one of the DNA mismatch repair proteins. The genes most frequently involved are MLH1, MHS2, and MSH6 with loss of function of one or more of the DNA repair proteins, typically an absence of protein(s). Consequently, immunohistochemistry (IHC) to assess expression of MLH1, MHS2, MHS6, and typically PMS2 can be used to infer the functional status of the DNA mismatch repair machinery. Alternatively, the tumor DNA can be evaluated for the sorts of mutations that accumulate when cells have lost DNA repair. A task force was convened to develop a standardized DNA testing approach to determine whether or not colon cancer cells have microsatellite instability [14]. A panel of markers, developed for colon cancer MSI analysis, has been widely adopted for the study of endometrial cancers. Both IHC and MSI analyses (DNA typing) are reliable measures of DNA mismatch repair status. However, neither is completely sensitive or specific. MSI typing gives a result that is based on the phenotypic manifestations of loss of DNA mismatch repair. IHC points to a biochemical defect that would be consistent with loss of DNA mismatch repair. These are distinct tests, each with limitations. As noted, methodologic differences related to how defects in DNA mismatch repair are evaluated could explain the different results reported for loss of DNA repair and outcome in uterine cancers. The current study by Arabi et al. assesses DNA mismatch repair status using IHC. The title of their paper, “Impact of Microsatellite Instability (MSI) on Survival in High Grade Endometrial Carcinoma,” suggests that the authors equate IHC findings with MSI. In truth, Arabi and colleagues did not measure microsatellite instability. In a much larger patient series, Cohn and colleagues used IHC to measure mismatch repair status and saw improved survival with intact DNA mismatch repair [8]. Although the patient populations studied were very different, the trends are similar. Other groups have measured microsatellite instability (DNA-based tumor phenotyping) and have reported improved survival of patients whose tumors lacked DNA mismatch repair or no difference in survival [10,11]. Comparing studies that use very different measurements of DNA mismatch repair status may be challenging. In the current study, Arabi et al. classify tumors as deficient in DNA mismatch repair (which they refer to a microsatellite unstable) if two of three immuno-markers fail to stain. They justify the use of these two of three-negative criteria as “microsatellite unstable” by comparing it to a DNA-based analysis in which two of five marker abnormalities are considered MSI-positive [15]. It is a leap of faith to equate IHC and DNA findings. In an ideal situation, both IHC and MSI typing would be performed. Not only is the relationship between IHC and MSI status uncertain for high grade tumors, the overall staining patterns for the three
152
Editorial
proteins studied are not well understood. The presentation of the data in the current paper does not allow for comparisons with previous studies. There are very predictable patterns of staining for MHS2 and MSH6, depending on the underlying molecular lesion. Loss of MSH2 due to a mutation in MSH2 is frequently associated with loss of immunodetectable MSH2 and MSH6 proteins. Mutation in MSH6, not an infrequent event in endometrial cancers [15,16], is associated with loss of MSH6 but persistence of MSH2 staining. MLH1 defects are usually associated with loss of both MLH1 and PMS2 protein. Triple negative tumors (no detectable MLH1, MSH2, and MSH6) are uncommon. It would be very interesting to know the IHC status of each mismatch repair protein in the individual tumors and to include PMS2 staining. The results of the current paper are perplexing. It is generally believed type II tumors infrequently exhibit mismatch repair defects. Most studies to date on DNA repair defects in endometrial carcinoma have focused on populations that were largely Caucasian. In the current study, more than half of the patients are African American. One tantalizing explanation for the observed association between loss of immunodetectable DNA mismatch repair proteins and poor survival is that the racial makeup of the study population contributes substantially to tumor biology. Additional population-based studies on the clinicopathologic significance of loss of DNA mismatch repair are warranted. How DNA mismatch repair defects are best measured is yet to be determined. The fact that IHC is already used in the clinical diagnostic laboratory setting suggests that this may be the best approach. Using clinic-ready methods in research paves the way for the rapid translation of research findings to clinical medicine. The jury is out on the prognostic significance of loss of DNA mismatch repair in uterine endometrial adenocarcinomas. References [1] Lengauer C, Kinzler KW, Vogelstein B. Genetic instabilites in human cancers. Nature 1998;396:643–9. [2] Hanahan D, Weinberg RA. The hallmarks of cancer. Cell 2000;100:57–70. [3] Loeb LA. Mutator phenotype may be required for multistage carcinogenesis. Cancer Research 1991;51:3075–9.
[4] Thibodeau SN, Bren G, Schaid D. Microsatellite instability in cancer of the proximal colon. Science 1993;260:816–9. [5] Aaltonen LA, Peltomaki P, Leach FS, Sistonen P, Pylkkanen L, Mecklin JP, et al. Clues to the pathogenesis of familial colorectal cancer. Science 1993;260:812–5. [6] Ionov Y, Peinado MA, Malkhosyan S, Shibata D, Perucho M. Ubiquitous somatic mutations in simple repeated sequences reveal a new mechanism for colonic carcinogenesis. Nature 1993;363:558–61. [7] Risinger JI, Berchuck A, Kohler MF, Watson P, Lynch HT, Boyd J. Genetic instability of microsatellites in endometrial carcinoma. Cancer Res 1993;53:5100–3. [8] Cohn DE, Frankel WL, Resnick KE, Zanagnolo VL, Copeland LJ, Hampel H, et al. Improved survival with an intact DNA mismatch repair system in endometrial cancer. Obstet Gynecol 2006 Nov;108(5):1208–15. [9] Maxwell GL, Risinger JI, Alvarez AA, Barrett JC, Berchuck A. Favorable survival associated with microsatellite instability in endometrioid endometrial cancers. Obstet Gynecol 2001;97(3):417–22. [10] Black D, Soslow RA, Levine DA, Tornos C, Chen SC, Hummer AJ, et al. Clinicopathologic significance of defective DNA mismatch repair in endometrial carcinoma. J Clin Oncol 2006 Apr. 10;24(11):1745–53. [11] Zighelboim I, Goodfellow PJ, Gao F, Gibb RK, Powell MA, Rader JS, et al. Microsatellite instability and epigenetic inactivation of MLH1 and outcome of patients with endometrial carcinomas of the endometrioid type. J Clin Oncol 2007 May 20;25(15):2042–8. [12] Catasus L, Machin P, Matias-Guiu X, Prat J. Microsatellite instability in endometrial carcinomas: clinicopathologic correlations in a series of 42 cases. Human Pathol 1998;29:1160–4. [13] Fiumicino S, Ercoli A, Ferrandina G, Hess P, Raspaglio G, Genuardi M, et al. Microsatellite instability is an independent indicator of recurrence in sporadic stage I-II endometrial adenocarcinoma. J Clin Oncol 2001;19(4):1008–14. [14] Boland CR, Thibodeau SN, Hamilton SR, Sidransky D, Eshleman JR, Burt RW, et al. A national cancer institute workshop on microsatellite instability for cancer detection and familial predisposition: development of international criteria for the determination of microsatellite instability in colorectal cancer. Cancer Res 1998;58(22):5248–57. [15] Goodfellow PJ, Buttin BM, Herzog TJ, Rader JS, Gibb RK, Swisher E, et al. Prevalence of defective DNA mismatch repair and MSH6 mutation in an unselected series of endometrial cancers. Proc Natl Acad Sci U S A 2003 May 13;100(10):5908–13. [16] Hampel H, Frankel W, Panescu J, Lockman J, Sotamaa K, Fix D, et al. Screening for Lynch syndrome (hereditary nonpolyposis colorectal cancer) among endometrial cancer patients. Cancer Res 2006 Aug 1;66(15):7810–7.
Paul J. Goodfellow Departments of Surgery and Obstetrics and Gynecology, Washington University School of Medicine, USA E-mail address: [email protected]. 13 March 2009
Contents lists available at ScienceDirect
Gynecologic Oncology j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / y g y n o
Editorial
Clinicopathologic significance of DNA mismatch repair defects in endometrial cancer: The devil is in the details Loss of genome stability is a feature of cancer cells [1,2]. The molecular and clinical progression of tumors depends on failures in normal DNA repair processes. The notion that tumor cells are hypermutable (have a so-called mutator phenotype) was first put forth by Loeb in 1991 [3] and loss of DNA mismatch repair (DMMR) was first described in human tumors in 1993 [4-7]. Naturally occurring strand slippage mutations in short repetitive elements go unrecognized in tumor cells that lack DMMR. The consequence is the accumulation of insertion and deletion mutations that are products of replication errors. Tumors with these sorts of abnormalities in repetitive DNA sequences have been referred to as RER-positive (replication error-positive). The DNA sequences most subject to strand slippage mutations are called microsatellites, and consequently the tumor abnormality that is detected is also referred to as microsatellite instability (MSI). Tumor cells lacking DNA mismatch repair accumulate mutations at a much higher rate than those with an intact mismatch repair system. Endometrial cancers frequently have defects in DNA mismatch repair with ∼25% of all endometrial cancers exhibiting the tumor DNA MSI-positive phenotype. The remaining 75% of tumors are referred to as microsatellite stable (MSS). Arabi and colleagues report the results of a study in which they assessed DNA mismatch repair status in high-grade endometrial cancers. Their analysis of 91 cases suggests that loss of DNA mismatch repair may be associated with adverse outcomes. This is an interesting finding, with clear clinical implications. It is also somewhat unexpected. Previous work had suggested that loss of DNA mismatch repair is associated with poor outcomes [8], improved outcomes [9,10], or similar outcomes relative to MSS cases [11]. It is important to consider the similarities and differences between the studies that have been reported to date, particularly the molecular approaches to measuring defects in DNA mismatch repair and the patient populations being investigated. There are several explanations for why studies might differ with respect to their conclusions regarding the clinical significance of loss of DNA mismatch repair. The underlying heterogeneity of patient populations is likely to explain some of the differences. Work by Arabi and colleagues presented in this issue of Gynecologic Oncology is a single-institution study for which efforts were made to capture all patients of interest. One caveat, however, is that only high-grade endometrial carcinomas were studied. The authors evaluated both type I (endometrioid) and type II (non-endometrioid) cancers. Other studies have been based on relatively small series or surveying loss of mismatch repair in different histologic types, while others have studied all histologic subtypes of uterine cancer and still others have focused on endometrioid cancers only [8,10-13]. The methods used to assess loss of DNA mismatch repair could also explain some of the variability in the results reported to date. As 0090-8258/$ – see front matter © 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.ygyno.2009.03.013
noted, loss of DNA mismatch repair results in accumulation of mutations in microsatellite sequences leading to MSI-positive tumors. The underlying molecular defect is the loss of function of one of the DNA mismatch repair proteins. The genes most frequently involved are MLH1, MHS2, and MSH6 with loss of function of one or more of the DNA repair proteins, typically an absence of protein(s). Consequently, immunohistochemistry (IHC) to assess expression of MLH1, MHS2, MHS6, and typically PMS2 can be used to infer the functional status of the DNA mismatch repair machinery. Alternatively, the tumor DNA can be evaluated for the sorts of mutations that accumulate when cells have lost DNA repair. A task force was convened to develop a standardized DNA testing approach to determine whether or not colon cancer cells have microsatellite instability [14]. A panel of markers, developed for colon cancer MSI analysis, has been widely adopted for the study of endometrial cancers. Both IHC and MSI analyses (DNA typing) are reliable measures of DNA mismatch repair status. However, neither is completely sensitive or specific. MSI typing gives a result that is based on the phenotypic manifestations of loss of DNA mismatch repair. IHC points to a biochemical defect that would be consistent with loss of DNA mismatch repair. These are distinct tests, each with limitations. As noted, methodologic differences related to how defects in DNA mismatch repair are evaluated could explain the different results reported for loss of DNA repair and outcome in uterine cancers. The current study by Arabi et al. assesses DNA mismatch repair status using IHC. The title of their paper, “Impact of Microsatellite Instability (MSI) on Survival in High Grade Endometrial Carcinoma,” suggests that the authors equate IHC findings with MSI. In truth, Arabi and colleagues did not measure microsatellite instability. In a much larger patient series, Cohn and colleagues used IHC to measure mismatch repair status and saw improved survival with intact DNA mismatch repair [8]. Although the patient populations studied were very different, the trends are similar. Other groups have measured microsatellite instability (DNA-based tumor phenotyping) and have reported improved survival of patients whose tumors lacked DNA mismatch repair or no difference in survival [10,11]. Comparing studies that use very different measurements of DNA mismatch repair status may be challenging. In the current study, Arabi et al. classify tumors as deficient in DNA mismatch repair (which they refer to a microsatellite unstable) if two of three immuno-markers fail to stain. They justify the use of these two of three-negative criteria as “microsatellite unstable” by comparing it to a DNA-based analysis in which two of five marker abnormalities are considered MSI-positive [15]. It is a leap of faith to equate IHC and DNA findings. In an ideal situation, both IHC and MSI typing would be performed. Not only is the relationship between IHC and MSI status uncertain for high grade tumors, the overall staining patterns for the three
152
Editorial
proteins studied are not well understood. The presentation of the data in the current paper does not allow for comparisons with previous studies. There are very predictable patterns of staining for MHS2 and MSH6, depending on the underlying molecular lesion. Loss of MSH2 due to a mutation in MSH2 is frequently associated with loss of immunodetectable MSH2 and MSH6 proteins. Mutation in MSH6, not an infrequent event in endometrial cancers [15,16], is associated with loss of MSH6 but persistence of MSH2 staining. MLH1 defects are usually associated with loss of both MLH1 and PMS2 protein. Triple negative tumors (no detectable MLH1, MSH2, and MSH6) are uncommon. It would be very interesting to know the IHC status of each mismatch repair protein in the individual tumors and to include PMS2 staining. The results of the current paper are perplexing. It is generally believed type II tumors infrequently exhibit mismatch repair defects. Most studies to date on DNA repair defects in endometrial carcinoma have focused on populations that were largely Caucasian. In the current study, more than half of the patients are African American. One tantalizing explanation for the observed association between loss of immunodetectable DNA mismatch repair proteins and poor survival is that the racial makeup of the study population contributes substantially to tumor biology. Additional population-based studies on the clinicopathologic significance of loss of DNA mismatch repair are warranted. How DNA mismatch repair defects are best measured is yet to be determined. The fact that IHC is already used in the clinical diagnostic laboratory setting suggests that this may be the best approach. Using clinic-ready methods in research paves the way for the rapid translation of research findings to clinical medicine. The jury is out on the prognostic significance of loss of DNA mismatch repair in uterine endometrial adenocarcinomas. References [1] Lengauer C, Kinzler KW, Vogelstein B. Genetic instabilites in human cancers. Nature 1998;396:643–9. [2] Hanahan D, Weinberg RA. The hallmarks of cancer. Cell 2000;100:57–70. [3] Loeb LA. Mutator phenotype may be required for multistage carcinogenesis. Cancer Research 1991;51:3075–9.
[4] Thibodeau SN, Bren G, Schaid D. Microsatellite instability in cancer of the proximal colon. Science 1993;260:816–9. [5] Aaltonen LA, Peltomaki P, Leach FS, Sistonen P, Pylkkanen L, Mecklin JP, et al. Clues to the pathogenesis of familial colorectal cancer. Science 1993;260:812–5. [6] Ionov Y, Peinado MA, Malkhosyan S, Shibata D, Perucho M. Ubiquitous somatic mutations in simple repeated sequences reveal a new mechanism for colonic carcinogenesis. Nature 1993;363:558–61. [7] Risinger JI, Berchuck A, Kohler MF, Watson P, Lynch HT, Boyd J. Genetic instability of microsatellites in endometrial carcinoma. Cancer Res 1993;53:5100–3. [8] Cohn DE, Frankel WL, Resnick KE, Zanagnolo VL, Copeland LJ, Hampel H, et al. Improved survival with an intact DNA mismatch repair system in endometrial cancer. Obstet Gynecol 2006 Nov;108(5):1208–15. [9] Maxwell GL, Risinger JI, Alvarez AA, Barrett JC, Berchuck A. Favorable survival associated with microsatellite instability in endometrioid endometrial cancers. Obstet Gynecol 2001;97(3):417–22. [10] Black D, Soslow RA, Levine DA, Tornos C, Chen SC, Hummer AJ, et al. Clinicopathologic significance of defective DNA mismatch repair in endometrial carcinoma. J Clin Oncol 2006 Apr. 10;24(11):1745–53. [11] Zighelboim I, Goodfellow PJ, Gao F, Gibb RK, Powell MA, Rader JS, et al. Microsatellite instability and epigenetic inactivation of MLH1 and outcome of patients with endometrial carcinomas of the endometrioid type. J Clin Oncol 2007 May 20;25(15):2042–8. [12] Catasus L, Machin P, Matias-Guiu X, Prat J. Microsatellite instability in endometrial carcinomas: clinicopathologic correlations in a series of 42 cases. Human Pathol 1998;29:1160–4. [13] Fiumicino S, Ercoli A, Ferrandina G, Hess P, Raspaglio G, Genuardi M, et al. Microsatellite instability is an independent indicator of recurrence in sporadic stage I-II endometrial adenocarcinoma. J Clin Oncol 2001;19(4):1008–14. [14] Boland CR, Thibodeau SN, Hamilton SR, Sidransky D, Eshleman JR, Burt RW, et al. A national cancer institute workshop on microsatellite instability for cancer detection and familial predisposition: development of international criteria for the determination of microsatellite instability in colorectal cancer. Cancer Res 1998;58(22):5248–57. [15] Goodfellow PJ, Buttin BM, Herzog TJ, Rader JS, Gibb RK, Swisher E, et al. Prevalence of defective DNA mismatch repair and MSH6 mutation in an unselected series of endometrial cancers. Proc Natl Acad Sci U S A 2003 May 13;100(10):5908–13. [16] Hampel H, Frankel W, Panescu J, Lockman J, Sotamaa K, Fix D, et al. Screening for Lynch syndrome (hereditary nonpolyposis colorectal cancer) among endometrial cancer patients. Cancer Res 2006 Aug 1;66(15):7810–7.
Paul J. Goodfellow Departments of Surgery and Obstetrics and Gynecology, Washington University School of Medicine, USA E-mail address: [email protected]. 13 March 2009