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Chromosomal findings in cultured melanocytes from a giant congenital nevus
Chromosomal Findings in Cultured Melanocytes from a Giant Congenital Nevus P. Heimann, G. Ogur, C. De Busscher, R. Morandini, A. Libert, and E. Vamos
ABSTRACT: A giant congenital pigmented nevus was observed in a newborn male. A melanocyte culture was established from nevus fragments removed at age 6 days. Analysis of 136 metaphases harvested from the primary culture showed 74% normal mitoses, 22% polyploids, and 4% mitoses with chromosome rearrangements involving in particular lp, 12q, and 19p. In addition, the culture showed a high level of HLA-DR expression. Although histology showed no sign of malignancy, these findings may illustrate one of the first events which might eventually progress toward malignancy.
INTRODUCTION Giant congenital melanocytic nevi (GCMN) are birth defects of mostly sporadic occurrence, associated with a risk for malignant melanoma estimated to be approximately 4-6% [1, 2]. The prognosis for melanoma arising from GCMN is usually poor [2] except for cases developing in the neonatal period [3]. Very few chromosome studies have been reported in this particular type of pigmented lesion. We report the cytogenetic findings in cultured melanocytes derived from a GCMN in a newborn infant. CASE REPORT
The proband was a male neonate born to a 32-year-old mother and a 48-year-old father. Examination disclosed a giant darkly pigmented nevus involving the back from neck to buttocks (Fig. 1) and extending laterally to the thorax and abdomen. Some areas of this nevus presented several small dark nodules. Satellite nevi were also present on the buttocks and thighs. Neurologic investigations including electroencephalogram, brain ultrasounds, and magnetic resonance imaging were negative. The greatest part of the nevus was treated by extirpation and skin grafting performed on the sixth day of life. On that occasion, fragments of pigmented skin were sampled for histopathology and cell cultures.
From the Laboratory ofCytogenetics (P. H., G. O., C. D. B., E. V..), University Hospital Brugmann, and Laboratory of Oncology and Experimental Surgery (R. M., A. L.), Faculty of Medicine, Campus Erasme, Brussels, Belgium. Address reprint request to: E. Vamos, M.D., Laboratoire de Cytog6n~tique, HSpital Universitaire Brugmann, Place A. Van Gehuchten 4, 1020 Brussels, Belgium. Received July 28, 1992; accepted March 1, 1993.
Microscopic examination showed an infiltration of the dermis by regular nests or cords of nevus cells extending down to the reticular dermis and subcutaneous tissue. There was involvement of skin adnexae and, in the deeper part, these nevus cells displayed neuroid differentiation. These features fulfilled the histologic criteria for a GCMN. No sign of malignancy was observed in the numerous fragments examined. Cytofluorimetric analysis of expression of some of the melanoma-associated antigens by the cultured melanocytes showed that HLA-DR and DQ were expressed in 87.5 and 8.8% of those cells, respectively. Three months later, the remaining pigmented skin was removed. Histology was similar to that of the previous examination. Cell culture was attempted but failed to grow. The patient is now aged 2 years, and his clinical status is stable.
CYTOGENETIC ANALYSIS A melanocyte culture was initiated from nevus fragments. No growth factor was added. In the primary culture, diverse cellular morphologies of epithelial and fibroblastic types were observed, but cells with dendritic processes predominated. The latter were often pigmented and piled up in multilayered disorderly masses. Growth was very rapid at onset but was arrested at the sixth passage. G-banded chromosome preparations were made from peripheral blood lymphocytes (PBL) as well as from an aliquot of primary culture with actively dividing melanocytes, harvested 6 days after initiation. The karyotype from PBL was entirely normal: 46,XY. In cultured melanocytes, 136 metaphases were analyzed. Results are shown in Table 1. Thirty mitoses were polyploid; 15 of them were regular tetraploids. Chromosome rearrangements observed in six mitoses were each unique, but chromosome segment 19p was involved in 2 mitoses (Fig. 2). In the mitosis with a nonreciprocal translocation dic(1;5)(p22;p15), there was a large, faint staining
74 Cancer Genet Cytogenet 6 8 : 7 4 - 7 7 (1993) 0165-4608/93/$06.00
© 1993 Elsevier Science P u b l i s h i n g Co., Inc. 655 A v e n u e of the Americas, N e w York, NY 10010
Chromosomal Findings in a GMCN
75
\
Table 1
Chromosome findings in cultured melanocytes
No. of mitoses
Karyotype
100 15 15
46,XY 92 ,XXYY Polyploids with extensive chromosome fragmentation 45,XY,dic(17;22)(p13;p11) 46,XY,t(4;19)(q27;p13) 45,XY,dic(12;19)(q22;p13) 46,XY,dic(1;5)(p22;p15), + mar 47,XY,r(16), + 22 74,XYY,dic(X;12?)(q28;q?), + 3, + 10, + 11, - 12, - 13, + 14, - 17, + 18, + 19, +20, +mar
1 1 1
1 1 1
Figure 1 Patient with giant pigmented nevus. marker, which was tentatively interpreted as an isochromosome of part of lp (p32~pter?) (Fig. 3). DISCUSSION Whereas the patient had a normal constitutional karyotype in PBL, various chromosome anomalies were observed in the primary melanocytic culture from the nevus, including polyploidy (30 mitoses), aneuploidy (four mitoses), and rearrangements (six mitoses). Chromosome changes associated with malignant melanomas have been investigated exten-
sively. Most reports emphasize the nonrandom involvement of chromosomes l(p and c0, 2p, 3(p and CO, 6(p and c0, 7(p and q), 9p and 11p [4-12]. In addition to these most frequently reported chromosome changes, Parmiter et al. described a reciprocal translocation (1;19)(q23 ;p13) in three cases of malignant melanoma [9]. To our knowledge, five reports have dealt with chromosome studies of small congenital or acquired nevi as well as dysplastic nevi [5-7, 11, 12]. Of the 72 nevi thus studied, 10 showed chromosome rearrangements (one case with a constitutional translocation). These occurred more often in dysplastic than in c o m m o n nevi, but three of the c o m m o n nevi demonstrating cytogenetic anomalies exhibited concomitant growth factor activity [7]. Such a correlation between growth factor activity and abnormal cytogenetic findings in the absence of histologic evidence of cell atypia may be related to the malignant potential of such lesions. Cytogenetic data in GCMN have been reported only three times. The report of Padilla et al. [13] deals with a case of malignant melanoma arising in a GCMN. In 27 mitoses, 17 showed multiple clonal and nonclonal structural rearrangements, consistent with overt malignancy demonstrated by histologic examination. In contrast, Mancianti et al. [14] observed no chromosomal changes in two cases of malignant melanoma simulants arising in GCMN despite histologic features suggestive of malignancy. Among the cases studied by Cowan et al. [11], one was a dysplastic nevus arising in a GCMN from which a melanoma had previously been removed. Although clonal karyotypic changes were noted, there was no histologic evidence of malignancy; the investi-
Figure 2 Partial karyotype of two metaphases showing (A) t(4;19)(q27;p13) and (B) dic(12;19)(q22;p13). Arrows denote breakpoints.
A
B
i
~ii~ ¸¸¸ "4---
4
19
12
lg
Figure 3
F
20
Metaphase showing dic(l;5)(pZ;p15)
19
*
(arrow indicating breakpoints] and marker.
2.44.17
C h r o m o s o m a l F i n d i n g s in a GMCN
77
gators suggested that the melanocytes studied derived from "a seeding of the original t u m o r to the naevus." In our case, the d i s c r e p a n c y between histologic and cytogenetic data may be d u e to different sites of sampling of the fragments u s e d for histology a n d cell culture, respectively. Indeed, some darker nodules were present on the surface of the nevus a n d may represent p r e m a l i g n a n t lesions. In this respect, our patient c o u l d be c o m p a r e d with the patient of Workman et al. [3], in w h o m n o d u l e s of malignant m e l a n o m a arose from a giant nevus in the first months of life. This patient was well and still clinically disease-free 5 years after operation. It is unfortunate that this case was not cytogenetically investigated. It is noteworthy that two of the c h r o m o s o m e breakpoints involved in rearrangements (lp a n d 19p} in our patient are similar to those observed in malignant melanomas. Of particular interest is the finding in one mitosis of a marker that might be interpreted as an isochromosome d u p l i c a t i n g part of lp: from lp32 to lpter. In a m e l a n o m a cell line, Pedersen et al. [8] described a derivative chromosome 1 with duplication 1p22~pter. Two factors indicate the importance of c h r o m o s o m e 1 in development of melanomas. First, this chromosome is the one most frequently involved in rearrangements in melanomas. Second, the gene for the dysplastic nevus syndrome (DNS), an autosomal d o m i n a n t trait accounting for nearly 10% of h u m a n melanomas, has been m a p p e d to c h r o m o s o m e segment lp36 [15]. A m o n g the six structurally abnormal mitoses, two have a translocation involving the short arm of chromosome 19 (p137}. Rearrangements of 19p have been reported in pre-B acute lymphocytic leukemia, in T-cell leukemias, and in three cases of malignant m e l a n o m a [9]. Cytogenefic changes, even when clonal, may be associated w i t h n o n m a l i g n a n t tumors [16, 17]. Therefore, the chrom o s o m a l findings in the present case do not in themselves demonstrate the malignant potential of this GCMN. These findings, together w i t h the h i g h HLA-DR expression, however, may represent one of the early steps, preceding morphologic changes, w h i c h in some cases will eventually progress to m a l i g n a n t m e l a n o m a .
2. Mosher DB, Fitzpatrick TB, Ortonne JP, Yhori Y {1987}:Disorders of melanocytes. In: Dermatology in General Medicine, 3rd ed., TB Fitzpatrick, AZ Eisen, K Wolff, IM Friedberg, KF Austen, eds. McGraw-Hill, New York, pp. 902-914. 3. Workman ML, Kaye VN, Anderson PM, Cunningham BL (1992}: Malignant melanoma with evidence of maturation arising from a giant congenital nevocellular nevus. Ann Plast Surg 28: 381-385. 4. Becher R, Gibas Z, Sandberg AA {1983}:Chromosomes in malignant melanoma. Cancer Genet, Cytogenet 9:173-175. 5. Balaban GB, Herlyn M, Dupont Guerry IV, Bartolo R, Koprowski H, Clark WH, Nowell PC {1984): Cytogenetics of human melanoma and premalignant lesions. Cancer Genet Cytogenet 11:429-439. 6. Balaban GB, Herlyn M, Clark WH, Nowell PC (1966): Karyotypic evolution in human malignant melanoma. Cancer Genet Cytogenet 19:113-122. 7. Richmond A, Fine R, Murray D, Lawson DH, Priest JH (1986): Growth factor and cytogenetic abnormalities in cultured naevi and malignant melanoma. J Invest Dermatol 86:295-302. 8. Pedersen MI, Bennett JW, Wang (1986): Non random chromosome structural aberrations and oncngene loci in human malignant melanoma. Cancer Genet Cytogenet 20:11-27. 9. Parmiter AH, Balaban G, Herlyn M, Clark WH Jr, Nowell PC (1986): A t(1;19) chromosome translocation in 3 cases of human malignant melanoma. Cancer Res 46:1526-1529. 10. Priest JH, Phillips CN, Wang Y, Richmond A (1988): Chromosome and growth factor abnormalities in melanoma. Cancer Genet Cytogenet 35:253-261. 11. Cowan JM, Halaban R, Francke U. (1988): Cytogenetic analysis of melanocytes from premalignant nevi and melanomas. J Natl Cancer Inst 1988; 80:1159-1164. 12. Parmiter AH, Nowell PC (1988): The cytogenetics of human malignant melanoma and premalignant lesions. Cancer Treat Res 43:47-61. 13. Padilla RS, McConnell TS, Gribble JT, Smoot C (1988): Malignant melanoma arising in a giant congenital melanocytic nevus: A case report with cytogenetic and histopathologic analysis. Cancer 62:2589-2594.
REFERENCES
16. Sandberg AA (1988): The cytogenetic route of benign tumors. Cancer Genet Cytogenet 32:11-12.
1. Rhodes AR, Wood WC (1981): Nonepidermal origin of malignant melanoma associated with a giant congenital nevocellular nevus. Plast Reconstr Surg 58:48.
14. Mancianti ML, Clark WH, Hayes FA, Herlyn M (1990): Malignant melanoma simulants arising in congenital melanocytic nevi do not show experimental evidence for a malignant phenotype. Am J Pathol 136:817-829. 15. Bale SJ, Dracopoli NC, Tucker MA, Clark WH, et al. (1989): Mapping the gene for hereditary cutaneous malignant melanoma dysplastic nevus to chromosome I p. N Engl J Med 320:1367-1372.
17. Teyssier JR, Ferre D (1989) Frequent clonal chromosomal changes in human non-malignant tumors. Int J Cancer 44:828-832.
ABSTRACT: A giant congenital pigmented nevus was observed in a newborn male. A melanocyte culture was established from nevus fragments removed at age 6 days. Analysis of 136 metaphases harvested from the primary culture showed 74% normal mitoses, 22% polyploids, and 4% mitoses with chromosome rearrangements involving in particular lp, 12q, and 19p. In addition, the culture showed a high level of HLA-DR expression. Although histology showed no sign of malignancy, these findings may illustrate one of the first events which might eventually progress toward malignancy.
INTRODUCTION Giant congenital melanocytic nevi (GCMN) are birth defects of mostly sporadic occurrence, associated with a risk for malignant melanoma estimated to be approximately 4-6% [1, 2]. The prognosis for melanoma arising from GCMN is usually poor [2] except for cases developing in the neonatal period [3]. Very few chromosome studies have been reported in this particular type of pigmented lesion. We report the cytogenetic findings in cultured melanocytes derived from a GCMN in a newborn infant. CASE REPORT
The proband was a male neonate born to a 32-year-old mother and a 48-year-old father. Examination disclosed a giant darkly pigmented nevus involving the back from neck to buttocks (Fig. 1) and extending laterally to the thorax and abdomen. Some areas of this nevus presented several small dark nodules. Satellite nevi were also present on the buttocks and thighs. Neurologic investigations including electroencephalogram, brain ultrasounds, and magnetic resonance imaging were negative. The greatest part of the nevus was treated by extirpation and skin grafting performed on the sixth day of life. On that occasion, fragments of pigmented skin were sampled for histopathology and cell cultures.
From the Laboratory ofCytogenetics (P. H., G. O., C. D. B., E. V..), University Hospital Brugmann, and Laboratory of Oncology and Experimental Surgery (R. M., A. L.), Faculty of Medicine, Campus Erasme, Brussels, Belgium. Address reprint request to: E. Vamos, M.D., Laboratoire de Cytog6n~tique, HSpital Universitaire Brugmann, Place A. Van Gehuchten 4, 1020 Brussels, Belgium. Received July 28, 1992; accepted March 1, 1993.
Microscopic examination showed an infiltration of the dermis by regular nests or cords of nevus cells extending down to the reticular dermis and subcutaneous tissue. There was involvement of skin adnexae and, in the deeper part, these nevus cells displayed neuroid differentiation. These features fulfilled the histologic criteria for a GCMN. No sign of malignancy was observed in the numerous fragments examined. Cytofluorimetric analysis of expression of some of the melanoma-associated antigens by the cultured melanocytes showed that HLA-DR and DQ were expressed in 87.5 and 8.8% of those cells, respectively. Three months later, the remaining pigmented skin was removed. Histology was similar to that of the previous examination. Cell culture was attempted but failed to grow. The patient is now aged 2 years, and his clinical status is stable.
CYTOGENETIC ANALYSIS A melanocyte culture was initiated from nevus fragments. No growth factor was added. In the primary culture, diverse cellular morphologies of epithelial and fibroblastic types were observed, but cells with dendritic processes predominated. The latter were often pigmented and piled up in multilayered disorderly masses. Growth was very rapid at onset but was arrested at the sixth passage. G-banded chromosome preparations were made from peripheral blood lymphocytes (PBL) as well as from an aliquot of primary culture with actively dividing melanocytes, harvested 6 days after initiation. The karyotype from PBL was entirely normal: 46,XY. In cultured melanocytes, 136 metaphases were analyzed. Results are shown in Table 1. Thirty mitoses were polyploid; 15 of them were regular tetraploids. Chromosome rearrangements observed in six mitoses were each unique, but chromosome segment 19p was involved in 2 mitoses (Fig. 2). In the mitosis with a nonreciprocal translocation dic(1;5)(p22;p15), there was a large, faint staining
74 Cancer Genet Cytogenet 6 8 : 7 4 - 7 7 (1993) 0165-4608/93/$06.00
© 1993 Elsevier Science P u b l i s h i n g Co., Inc. 655 A v e n u e of the Americas, N e w York, NY 10010
Chromosomal Findings in a GMCN
75
\
Table 1
Chromosome findings in cultured melanocytes
No. of mitoses
Karyotype
100 15 15
46,XY 92 ,XXYY Polyploids with extensive chromosome fragmentation 45,XY,dic(17;22)(p13;p11) 46,XY,t(4;19)(q27;p13) 45,XY,dic(12;19)(q22;p13) 46,XY,dic(1;5)(p22;p15), + mar 47,XY,r(16), + 22 74,XYY,dic(X;12?)(q28;q?), + 3, + 10, + 11, - 12, - 13, + 14, - 17, + 18, + 19, +20, +mar
1 1 1
1 1 1
Figure 1 Patient with giant pigmented nevus. marker, which was tentatively interpreted as an isochromosome of part of lp (p32~pter?) (Fig. 3). DISCUSSION Whereas the patient had a normal constitutional karyotype in PBL, various chromosome anomalies were observed in the primary melanocytic culture from the nevus, including polyploidy (30 mitoses), aneuploidy (four mitoses), and rearrangements (six mitoses). Chromosome changes associated with malignant melanomas have been investigated exten-
sively. Most reports emphasize the nonrandom involvement of chromosomes l(p and c0, 2p, 3(p and CO, 6(p and c0, 7(p and q), 9p and 11p [4-12]. In addition to these most frequently reported chromosome changes, Parmiter et al. described a reciprocal translocation (1;19)(q23 ;p13) in three cases of malignant melanoma [9]. To our knowledge, five reports have dealt with chromosome studies of small congenital or acquired nevi as well as dysplastic nevi [5-7, 11, 12]. Of the 72 nevi thus studied, 10 showed chromosome rearrangements (one case with a constitutional translocation). These occurred more often in dysplastic than in c o m m o n nevi, but three of the c o m m o n nevi demonstrating cytogenetic anomalies exhibited concomitant growth factor activity [7]. Such a correlation between growth factor activity and abnormal cytogenetic findings in the absence of histologic evidence of cell atypia may be related to the malignant potential of such lesions. Cytogenetic data in GCMN have been reported only three times. The report of Padilla et al. [13] deals with a case of malignant melanoma arising in a GCMN. In 27 mitoses, 17 showed multiple clonal and nonclonal structural rearrangements, consistent with overt malignancy demonstrated by histologic examination. In contrast, Mancianti et al. [14] observed no chromosomal changes in two cases of malignant melanoma simulants arising in GCMN despite histologic features suggestive of malignancy. Among the cases studied by Cowan et al. [11], one was a dysplastic nevus arising in a GCMN from which a melanoma had previously been removed. Although clonal karyotypic changes were noted, there was no histologic evidence of malignancy; the investi-
Figure 2 Partial karyotype of two metaphases showing (A) t(4;19)(q27;p13) and (B) dic(12;19)(q22;p13). Arrows denote breakpoints.
A
B
i
~ii~ ¸¸¸ "4---
4
19
12
lg
Figure 3
F
20
Metaphase showing dic(l;5)(pZ;p15)
19
*
(arrow indicating breakpoints] and marker.
2.44.17
C h r o m o s o m a l F i n d i n g s in a GMCN
77
gators suggested that the melanocytes studied derived from "a seeding of the original t u m o r to the naevus." In our case, the d i s c r e p a n c y between histologic and cytogenetic data may be d u e to different sites of sampling of the fragments u s e d for histology a n d cell culture, respectively. Indeed, some darker nodules were present on the surface of the nevus a n d may represent p r e m a l i g n a n t lesions. In this respect, our patient c o u l d be c o m p a r e d with the patient of Workman et al. [3], in w h o m n o d u l e s of malignant m e l a n o m a arose from a giant nevus in the first months of life. This patient was well and still clinically disease-free 5 years after operation. It is unfortunate that this case was not cytogenetically investigated. It is noteworthy that two of the c h r o m o s o m e breakpoints involved in rearrangements (lp a n d 19p} in our patient are similar to those observed in malignant melanomas. Of particular interest is the finding in one mitosis of a marker that might be interpreted as an isochromosome d u p l i c a t i n g part of lp: from lp32 to lpter. In a m e l a n o m a cell line, Pedersen et al. [8] described a derivative chromosome 1 with duplication 1p22~pter. Two factors indicate the importance of c h r o m o s o m e 1 in development of melanomas. First, this chromosome is the one most frequently involved in rearrangements in melanomas. Second, the gene for the dysplastic nevus syndrome (DNS), an autosomal d o m i n a n t trait accounting for nearly 10% of h u m a n melanomas, has been m a p p e d to c h r o m o s o m e segment lp36 [15]. A m o n g the six structurally abnormal mitoses, two have a translocation involving the short arm of chromosome 19 (p137}. Rearrangements of 19p have been reported in pre-B acute lymphocytic leukemia, in T-cell leukemias, and in three cases of malignant m e l a n o m a [9]. Cytogenefic changes, even when clonal, may be associated w i t h n o n m a l i g n a n t tumors [16, 17]. Therefore, the chrom o s o m a l findings in the present case do not in themselves demonstrate the malignant potential of this GCMN. These findings, together w i t h the h i g h HLA-DR expression, however, may represent one of the early steps, preceding morphologic changes, w h i c h in some cases will eventually progress to m a l i g n a n t m e l a n o m a .
2. Mosher DB, Fitzpatrick TB, Ortonne JP, Yhori Y {1987}:Disorders of melanocytes. In: Dermatology in General Medicine, 3rd ed., TB Fitzpatrick, AZ Eisen, K Wolff, IM Friedberg, KF Austen, eds. McGraw-Hill, New York, pp. 902-914. 3. Workman ML, Kaye VN, Anderson PM, Cunningham BL (1992}: Malignant melanoma with evidence of maturation arising from a giant congenital nevocellular nevus. Ann Plast Surg 28: 381-385. 4. Becher R, Gibas Z, Sandberg AA {1983}:Chromosomes in malignant melanoma. Cancer Genet, Cytogenet 9:173-175. 5. Balaban GB, Herlyn M, Dupont Guerry IV, Bartolo R, Koprowski H, Clark WH, Nowell PC {1984): Cytogenetics of human melanoma and premalignant lesions. Cancer Genet Cytogenet 11:429-439. 6. Balaban GB, Herlyn M, Clark WH, Nowell PC (1966): Karyotypic evolution in human malignant melanoma. Cancer Genet Cytogenet 19:113-122. 7. Richmond A, Fine R, Murray D, Lawson DH, Priest JH (1986): Growth factor and cytogenetic abnormalities in cultured naevi and malignant melanoma. J Invest Dermatol 86:295-302. 8. Pedersen MI, Bennett JW, Wang (1986): Non random chromosome structural aberrations and oncngene loci in human malignant melanoma. Cancer Genet Cytogenet 20:11-27. 9. Parmiter AH, Balaban G, Herlyn M, Clark WH Jr, Nowell PC (1986): A t(1;19) chromosome translocation in 3 cases of human malignant melanoma. Cancer Res 46:1526-1529. 10. Priest JH, Phillips CN, Wang Y, Richmond A (1988): Chromosome and growth factor abnormalities in melanoma. Cancer Genet Cytogenet 35:253-261. 11. Cowan JM, Halaban R, Francke U. (1988): Cytogenetic analysis of melanocytes from premalignant nevi and melanomas. J Natl Cancer Inst 1988; 80:1159-1164. 12. Parmiter AH, Nowell PC (1988): The cytogenetics of human malignant melanoma and premalignant lesions. Cancer Treat Res 43:47-61. 13. Padilla RS, McConnell TS, Gribble JT, Smoot C (1988): Malignant melanoma arising in a giant congenital melanocytic nevus: A case report with cytogenetic and histopathologic analysis. Cancer 62:2589-2594.
REFERENCES
16. Sandberg AA (1988): The cytogenetic route of benign tumors. Cancer Genet Cytogenet 32:11-12.
1. Rhodes AR, Wood WC (1981): Nonepidermal origin of malignant melanoma associated with a giant congenital nevocellular nevus. Plast Reconstr Surg 58:48.
14. Mancianti ML, Clark WH, Hayes FA, Herlyn M (1990): Malignant melanoma simulants arising in congenital melanocytic nevi do not show experimental evidence for a malignant phenotype. Am J Pathol 136:817-829. 15. Bale SJ, Dracopoli NC, Tucker MA, Clark WH, et al. (1989): Mapping the gene for hereditary cutaneous malignant melanoma dysplastic nevus to chromosome I p. N Engl J Med 320:1367-1372.
17. Teyssier JR, Ferre D (1989) Frequent clonal chromosomal changes in human non-malignant tumors. Int J Cancer 44:828-832.