- Email: [email protected]
“AT risk” for breast cancer
THE LANCET
COMMENTARY demonstrated in AT heterozygote cell-lines, but clear evidence of abnormal DNA processing in the Although it is now known that the BRCA1 and BRCA2 heterozygote is not forthcoming. A second mechanism genes account for fewer than 10% of all breast-cancer would involve a somatic loss of heterozygosity at the AT cases, women with neither of these genes often give a locus, whereby the one functional allele is lost. Such an family history of the disease. Moreover, first-degree event would generate a clone that has the complete AT relatives of women with breast cancer have increased risk phenotype, which would then accumulate mutations at an of developing the disorder. Hence other, commoner, but increased rate, making malignant transformation more less penetrant and poorly defined heritable factors are likely. Numerous studies have yielded evidence suggestive 1 probably involved in breast cancer. The ataxia of loss of heterozygosity in the region of ATM on telangiectasia gene (ATM) has been thought to be a chromosome 11q22-23.5 However, this region is gene 2 candidate. However, Fitzgerald and colleagues, who rich, and the evidence tends to rule out ATM as a screened ATM for mutations in more than 400 women frequently lost tumour-suppressor gene. Neither with early-onset breast cancer, have found no evidence for mechanism explains why AT heterozygosity should affect such a role for the gene in such cases. Where does this breast tissue prerferentially, but the association would leave the oft-cited association between ataxia help account for the increased incidence of breast cancer telangiectasia (AT) and breast cancer? in atom-bomb survivors and women irradiated for About 20 years ago Swift reported data suggestive of a Hodgkin’s disease6 and would support suggestions of a six-fold increased risk of breast cancer in women in AT potentially radiosensitive subgroup among breast-cancer families.3 Verifying this finding has been difficult because patients. AT carriers, who may comprise 1% of the population, Given the substantial circumstantial evidence linking have no clinical phenotype and lack distinguishing in-vitro AT to breast cancer, what is to be made of the Fitzgerald cellular characteristics. ATM was cloned and sequenced study? Out of 400 early-onset breast-cancer patients in 1995, but its size and complexity as well as its lack of screened, only two mutations (representing 0·5% of the mutational hotspots preclude the development of a simple group) were found in ATM, fewer than in the normal and rapid diagnostic test. To date, the most promising population analysed. It may be that ATM has nothing to cDNA screening approach seems to be the proteindo with breast cancer, in which case Swift’s original and truncation-based method, believed to detect about subsequent data still needs explaining. There is the 60–70% of ATM mutations,4 and used by Fitzgerald’s possibility that ATM has little to do with early-onset group. breast cancer because the predisposition it confers A relation between AT and cancer is not in question becomes apparent only in later life. Alternatively, the (panel). What though of the AT heterozygote? How might association may be real but was not statistically the inheritance of one defective AT gene predispose to demonstrated in the study, which has a 40% chance of cancer? The answer to this is not clear. Only one study, detecting a fourfold increase in risk and only a 6% chance using molecular techniques, has shown inheritance of of detecting a twofold increase. ATM in cancer-prone families. If AT heterozygosity does Another important issue is that the protein-truncation predispose to cancer, perhaps one of two potential assay detects, at most, 75% of ATM mutations. In mechanisms may be responsible. addition, this assay has been most successful in detecting The first assumes that AT heterozygosity represents a mutations in heterozygote AT patients. If, for some milder mutator phenotype than the homozygote, but one reason, the abnormal gene is not expressed in such that would still accumulate mutations more rapidly than individuals, then the protein-truncation test would not normal individuals. Accumulating the required number of detect heterozygotes. What the Fitzgerald study highlights hits should, therefore, be a stochastic phenomenon taking is the difficulty inherent in screening a population for longer than in the homozygote so that the predisposition unknown ATM mutations. Another study that followed becomes apparent only after the 5th and 6th decades. A specific mutational markers among AT families was able slight increased sensitivity to radiation has been to confirm a relative risk of 3·8 of developing breast cancer among AT carriers,7 Evidence linking AT with cancer which suggests that the association is real but Clinically, AT patients have a strong predisposition to lymphoreticular malignancies difficult to confirm by screening in their first 2 decades of life and to solid tumours if they sur vive beyond that.8 a population for unknown Vir tually all ATM knock-out mice develop thymic lymophomas by 4 months of age. mutations. Confirming the Swift At the molecular level, the full-blown AT phenotype affects two key aspects of hypothesis has many genomic DNA management that lead to an increased probability of mutation implications for understanding accumulation: breast cancer. First, it would 䢇 AT cells fail to induce appropriate p53 expression in response to ionising radiation, identify ATM as a common but 9 so that the cell-cycle arrest that normally allows for DNA repair is lost; not fully penetrant heritable 䢇 Aaberrant V(D)J recombinase activity (the enzyme responsible for the rearranging factor, shedding new light on the of T-cell receptor and immunoglobulin genes) has been documented in AT cells, aetiology of “sporadic” breast which suggests that somatic recombinator y processes are also affected.10 cancer. It would confirm that DNA repair and processing Consequently, AT cells are likely to represent a mutator phenotype that can acquire deficiencies, already implicated the many genomic hits required for full malignant transformation. in the aetiology of colon cancer,
“AT risk” for breast cancer
1784
Vol 349 • June 21, 1997
THE LANCET
COMMENTARY have a role in breast carcinogenesis as well. It would also raise issues of lifestyle counselling and management for those identified as AT heterozygotes and would identify the need for detailed research into the effect of routine procedures such as chest and dental radiographs, mammography, and radiation treatment in such individuals. If it is shown that loss of heterozygosity at the AT locus occurs in a proportion of breast tumours, then the resultant AT homozygous malignant clone should be very sensitive to radiation or radiomimetic chemical agents and would be best managed accordingly. This point raises the intriguing possibility of future cancer treatments being dictated by the patient’s and the tumour’s genetic makeup. Clearly, the issue of AT heterozygosity and breast cancer is highly significant and requires clarification. Fitzgerald et al’s study represents a significant step toward this end but by no means is it the final word. A similar study screening an older patient group is the next logical step, followed, possibly, by a large DNA sequencing exercise that will define the precise role of ATM in breast cancer.
Gwyn Bebb, Barr y Glickman, Karen Gelmon, Richard Gatti Depar tment of Advanced Therapeutics, British Columbia Cancer Agency, Vancouver, BC, V5Z 4E6, Canada; Centre for Environmental Health, University of Victoria, Victoria, BC; and Depar tment of Pathology, University of California, Los Angeles, California,, USA 1
Easton DF, Ford D. The genetics of breast and ovarian cancer. Br J Cancer 1995; 72: 805–12. 2 Fitzgerald MG, Bean JM, Hegde SR, et al. Heterozygous ATM mutations do not contribute to early onset of breast cancer. Nat Genet 1997; 15: 307-10. 3 Swift M, Morrell D, Massey RB, Chase CL. Incidence of cancer in 161 families affected by ataxia-telangiectasia. N Engl J Med 1991; 325: 1831–36. 4 Telatar M, Wang Z, Udar N, et al. Ataxia telangiectasia: mutations in ATM cDNA detected by protein truncation screening. Am J Hum Genet 1996; 59: 40–44. 5 Tomlinson IP, Strickland JE, Lee AS, et al. Loss of heterozygosity on chromosome 11Q in breast cancer. J Clin Pathol 1995; 48: 424-28. 6 Bhatia S, Robison LL, Oberlin O, et al. Breast and other second neoplasms after childhood Hodgkin’s disease. N Engl J Med 1996; 334: 745–51. 7 Athma P, Rappaport R, Swift M. Cancer Genet Cytogenet 1996; 92: 130–34. 8 Gatti, Boder E, Vintners HV, Sparkes RS, normal A, lange K. Atazia telangiectasis: An interdisciplinary approach to pathogenesis. Medicine 1991; 70: 99-117. 9 Kastan MB, Zhan Q, El-Deiry WA, et al. A mammalian cell cycle checkpoint pathway utilising p53 and GADD45 is defective in ataxia telangiectasia. Cell 1992; 74: 353-40. 10 Kirsch IR. V(d)J recombination and ataxia-telangiectasia: A review. Int J Radiat Biol 1994: 66: S97-108.
Unanswered questions in carcinoma of the testis Carcinoma of the testis has increased in incidence progressively during the past four decades and is now the commonest carcinoma of young men. The incidence varies geographically even between contiguous countries. The increase has been greatest in Denmark, where it affects 1% of young men. The prevalence remains much lower in neighbouring Finland. This difference raises the possibility of an environmental factor as the prime cause. There are many unsolved problems. Why are there two age peaks of testicular cancer—one in early postnatal life and one in the 20s? Why is cancer commoner in
Vol 349 • June 21, 1997
undescended testes, or when there is gonadal dysgenesis or the androgen insensitivity syndrome? At least 10% of men with a maldescended testis develop testicular carcinoma in situ, the percentage rising to about 40% if the maldescended testis is also atrophic. Why is there also a negative correlation with sperm density? Why do Scandinavian men born during the 1939-45 war have a lower risk whereas low birth weight is associated with an increased risk? Why is the risk increased in the contralateral testis? These and other aspects were discussed last month in Copenhagen at an international workshop organised by Neils Skakkeback, University of Copenhagen. Over 95% of patients with testicular cancer can now be cured. However, the radiation and chemotherapy usually given after surgery inevitably affect the remaining testis. The subsequent fertility of men who are childless or have not completed their family has therefore become an increasing problem. Should the remaining testis, in which the incidence of carcinoma in situ is increased, be merely “watched”, at the risk of uncontrolled neoplastic spread, or should radiotherapy and chemotherapy, which will cause permanent sterility, be given forthwith? Cryopreservation of sperm before definitive therapy may not necessarily solve the problem. However, the successful transplantation of testicular tissue in mice1 and more recently, as presented at Copenhagen by Li Jiang and Roger Short from Melbourne, from Sprague Dawley to Long Evans rats, has obvious clinical implication. Male primordial germ cells should in fact be simpler to transplant than ovarian tissue, in which the oocyte pool is limited and adversely affected by ageing. The search for a possible genetic basis has involved families in which testicular cancer is six to ten times commoner than in the normal population. A multinational chromosomal study in over 100 such families coordinated by the UK Imperial Cancer Research Fund has revealed considerable genetic heterogeneity. Nevertheless, there is no evidence of one genomic region, only several “candidate” regions. When is the stage set for development of testicular carcinoma in situ? The early postnatal peak incidence, the link with a birth cohort, and the association with testicular maldevelopment, suggest a critical prenatal influence. The possibility that cellular change occurs in the course of migration of primordial germ cells to the genital region was raised by Peter Donovan (Frederick, USA). Gloria Callard (Boston, USA) suggested that invasive potential might be induced even before meiosis. The increased endocrine activity associated with gonadotropin stimulation, postnatally and around puberty, was also considered a critical stimulus for revealing the malignant potential of primordial germ cells. It is therefore relevant that testicular cancer is rare in men with hypogonadotrophic hypogonadism, who have an increased risk of undescended testes. Testicular biopsies from untreated men with hypogonadotrophic hypogonadism have shown undifferentiated Sertoli cells and absence of spermatogenesis. Could stimulation of Sertoli cells during puberty, when endocrine activity increases, be linked with the subsequent development of testicular cancer? Could an inhibin also be involved? It is of interest, as Skakkeback reported, that inhibin B is not detectable in boys with anorchia and that newborn boys 1785
COMMENTARY demonstrated in AT heterozygote cell-lines, but clear evidence of abnormal DNA processing in the Although it is now known that the BRCA1 and BRCA2 heterozygote is not forthcoming. A second mechanism genes account for fewer than 10% of all breast-cancer would involve a somatic loss of heterozygosity at the AT cases, women with neither of these genes often give a locus, whereby the one functional allele is lost. Such an family history of the disease. Moreover, first-degree event would generate a clone that has the complete AT relatives of women with breast cancer have increased risk phenotype, which would then accumulate mutations at an of developing the disorder. Hence other, commoner, but increased rate, making malignant transformation more less penetrant and poorly defined heritable factors are likely. Numerous studies have yielded evidence suggestive 1 probably involved in breast cancer. The ataxia of loss of heterozygosity in the region of ATM on telangiectasia gene (ATM) has been thought to be a chromosome 11q22-23.5 However, this region is gene 2 candidate. However, Fitzgerald and colleagues, who rich, and the evidence tends to rule out ATM as a screened ATM for mutations in more than 400 women frequently lost tumour-suppressor gene. Neither with early-onset breast cancer, have found no evidence for mechanism explains why AT heterozygosity should affect such a role for the gene in such cases. Where does this breast tissue prerferentially, but the association would leave the oft-cited association between ataxia help account for the increased incidence of breast cancer telangiectasia (AT) and breast cancer? in atom-bomb survivors and women irradiated for About 20 years ago Swift reported data suggestive of a Hodgkin’s disease6 and would support suggestions of a six-fold increased risk of breast cancer in women in AT potentially radiosensitive subgroup among breast-cancer families.3 Verifying this finding has been difficult because patients. AT carriers, who may comprise 1% of the population, Given the substantial circumstantial evidence linking have no clinical phenotype and lack distinguishing in-vitro AT to breast cancer, what is to be made of the Fitzgerald cellular characteristics. ATM was cloned and sequenced study? Out of 400 early-onset breast-cancer patients in 1995, but its size and complexity as well as its lack of screened, only two mutations (representing 0·5% of the mutational hotspots preclude the development of a simple group) were found in ATM, fewer than in the normal and rapid diagnostic test. To date, the most promising population analysed. It may be that ATM has nothing to cDNA screening approach seems to be the proteindo with breast cancer, in which case Swift’s original and truncation-based method, believed to detect about subsequent data still needs explaining. There is the 60–70% of ATM mutations,4 and used by Fitzgerald’s possibility that ATM has little to do with early-onset group. breast cancer because the predisposition it confers A relation between AT and cancer is not in question becomes apparent only in later life. Alternatively, the (panel). What though of the AT heterozygote? How might association may be real but was not statistically the inheritance of one defective AT gene predispose to demonstrated in the study, which has a 40% chance of cancer? The answer to this is not clear. Only one study, detecting a fourfold increase in risk and only a 6% chance using molecular techniques, has shown inheritance of of detecting a twofold increase. ATM in cancer-prone families. If AT heterozygosity does Another important issue is that the protein-truncation predispose to cancer, perhaps one of two potential assay detects, at most, 75% of ATM mutations. In mechanisms may be responsible. addition, this assay has been most successful in detecting The first assumes that AT heterozygosity represents a mutations in heterozygote AT patients. If, for some milder mutator phenotype than the homozygote, but one reason, the abnormal gene is not expressed in such that would still accumulate mutations more rapidly than individuals, then the protein-truncation test would not normal individuals. Accumulating the required number of detect heterozygotes. What the Fitzgerald study highlights hits should, therefore, be a stochastic phenomenon taking is the difficulty inherent in screening a population for longer than in the homozygote so that the predisposition unknown ATM mutations. Another study that followed becomes apparent only after the 5th and 6th decades. A specific mutational markers among AT families was able slight increased sensitivity to radiation has been to confirm a relative risk of 3·8 of developing breast cancer among AT carriers,7 Evidence linking AT with cancer which suggests that the association is real but Clinically, AT patients have a strong predisposition to lymphoreticular malignancies difficult to confirm by screening in their first 2 decades of life and to solid tumours if they sur vive beyond that.8 a population for unknown Vir tually all ATM knock-out mice develop thymic lymophomas by 4 months of age. mutations. Confirming the Swift At the molecular level, the full-blown AT phenotype affects two key aspects of hypothesis has many genomic DNA management that lead to an increased probability of mutation implications for understanding accumulation: breast cancer. First, it would 䢇 AT cells fail to induce appropriate p53 expression in response to ionising radiation, identify ATM as a common but 9 so that the cell-cycle arrest that normally allows for DNA repair is lost; not fully penetrant heritable 䢇 Aaberrant V(D)J recombinase activity (the enzyme responsible for the rearranging factor, shedding new light on the of T-cell receptor and immunoglobulin genes) has been documented in AT cells, aetiology of “sporadic” breast which suggests that somatic recombinator y processes are also affected.10 cancer. It would confirm that DNA repair and processing Consequently, AT cells are likely to represent a mutator phenotype that can acquire deficiencies, already implicated the many genomic hits required for full malignant transformation. in the aetiology of colon cancer,
“AT risk” for breast cancer
1784
Vol 349 • June 21, 1997
THE LANCET
COMMENTARY have a role in breast carcinogenesis as well. It would also raise issues of lifestyle counselling and management for those identified as AT heterozygotes and would identify the need for detailed research into the effect of routine procedures such as chest and dental radiographs, mammography, and radiation treatment in such individuals. If it is shown that loss of heterozygosity at the AT locus occurs in a proportion of breast tumours, then the resultant AT homozygous malignant clone should be very sensitive to radiation or radiomimetic chemical agents and would be best managed accordingly. This point raises the intriguing possibility of future cancer treatments being dictated by the patient’s and the tumour’s genetic makeup. Clearly, the issue of AT heterozygosity and breast cancer is highly significant and requires clarification. Fitzgerald et al’s study represents a significant step toward this end but by no means is it the final word. A similar study screening an older patient group is the next logical step, followed, possibly, by a large DNA sequencing exercise that will define the precise role of ATM in breast cancer.
Gwyn Bebb, Barr y Glickman, Karen Gelmon, Richard Gatti Depar tment of Advanced Therapeutics, British Columbia Cancer Agency, Vancouver, BC, V5Z 4E6, Canada; Centre for Environmental Health, University of Victoria, Victoria, BC; and Depar tment of Pathology, University of California, Los Angeles, California,, USA 1
Easton DF, Ford D. The genetics of breast and ovarian cancer. Br J Cancer 1995; 72: 805–12. 2 Fitzgerald MG, Bean JM, Hegde SR, et al. Heterozygous ATM mutations do not contribute to early onset of breast cancer. Nat Genet 1997; 15: 307-10. 3 Swift M, Morrell D, Massey RB, Chase CL. Incidence of cancer in 161 families affected by ataxia-telangiectasia. N Engl J Med 1991; 325: 1831–36. 4 Telatar M, Wang Z, Udar N, et al. Ataxia telangiectasia: mutations in ATM cDNA detected by protein truncation screening. Am J Hum Genet 1996; 59: 40–44. 5 Tomlinson IP, Strickland JE, Lee AS, et al. Loss of heterozygosity on chromosome 11Q in breast cancer. J Clin Pathol 1995; 48: 424-28. 6 Bhatia S, Robison LL, Oberlin O, et al. Breast and other second neoplasms after childhood Hodgkin’s disease. N Engl J Med 1996; 334: 745–51. 7 Athma P, Rappaport R, Swift M. Cancer Genet Cytogenet 1996; 92: 130–34. 8 Gatti, Boder E, Vintners HV, Sparkes RS, normal A, lange K. Atazia telangiectasis: An interdisciplinary approach to pathogenesis. Medicine 1991; 70: 99-117. 9 Kastan MB, Zhan Q, El-Deiry WA, et al. A mammalian cell cycle checkpoint pathway utilising p53 and GADD45 is defective in ataxia telangiectasia. Cell 1992; 74: 353-40. 10 Kirsch IR. V(d)J recombination and ataxia-telangiectasia: A review. Int J Radiat Biol 1994: 66: S97-108.
Unanswered questions in carcinoma of the testis Carcinoma of the testis has increased in incidence progressively during the past four decades and is now the commonest carcinoma of young men. The incidence varies geographically even between contiguous countries. The increase has been greatest in Denmark, where it affects 1% of young men. The prevalence remains much lower in neighbouring Finland. This difference raises the possibility of an environmental factor as the prime cause. There are many unsolved problems. Why are there two age peaks of testicular cancer—one in early postnatal life and one in the 20s? Why is cancer commoner in
Vol 349 • June 21, 1997
undescended testes, or when there is gonadal dysgenesis or the androgen insensitivity syndrome? At least 10% of men with a maldescended testis develop testicular carcinoma in situ, the percentage rising to about 40% if the maldescended testis is also atrophic. Why is there also a negative correlation with sperm density? Why do Scandinavian men born during the 1939-45 war have a lower risk whereas low birth weight is associated with an increased risk? Why is the risk increased in the contralateral testis? These and other aspects were discussed last month in Copenhagen at an international workshop organised by Neils Skakkeback, University of Copenhagen. Over 95% of patients with testicular cancer can now be cured. However, the radiation and chemotherapy usually given after surgery inevitably affect the remaining testis. The subsequent fertility of men who are childless or have not completed their family has therefore become an increasing problem. Should the remaining testis, in which the incidence of carcinoma in situ is increased, be merely “watched”, at the risk of uncontrolled neoplastic spread, or should radiotherapy and chemotherapy, which will cause permanent sterility, be given forthwith? Cryopreservation of sperm before definitive therapy may not necessarily solve the problem. However, the successful transplantation of testicular tissue in mice1 and more recently, as presented at Copenhagen by Li Jiang and Roger Short from Melbourne, from Sprague Dawley to Long Evans rats, has obvious clinical implication. Male primordial germ cells should in fact be simpler to transplant than ovarian tissue, in which the oocyte pool is limited and adversely affected by ageing. The search for a possible genetic basis has involved families in which testicular cancer is six to ten times commoner than in the normal population. A multinational chromosomal study in over 100 such families coordinated by the UK Imperial Cancer Research Fund has revealed considerable genetic heterogeneity. Nevertheless, there is no evidence of one genomic region, only several “candidate” regions. When is the stage set for development of testicular carcinoma in situ? The early postnatal peak incidence, the link with a birth cohort, and the association with testicular maldevelopment, suggest a critical prenatal influence. The possibility that cellular change occurs in the course of migration of primordial germ cells to the genital region was raised by Peter Donovan (Frederick, USA). Gloria Callard (Boston, USA) suggested that invasive potential might be induced even before meiosis. The increased endocrine activity associated with gonadotropin stimulation, postnatally and around puberty, was also considered a critical stimulus for revealing the malignant potential of primordial germ cells. It is therefore relevant that testicular cancer is rare in men with hypogonadotrophic hypogonadism, who have an increased risk of undescended testes. Testicular biopsies from untreated men with hypogonadotrophic hypogonadism have shown undifferentiated Sertoli cells and absence of spermatogenesis. Could stimulation of Sertoli cells during puberty, when endocrine activity increases, be linked with the subsequent development of testicular cancer? Could an inhibin also be involved? It is of interest, as Skakkeback reported, that inhibin B is not detectable in boys with anorchia and that newborn boys 1785