Nevus-Associated Melanomas
Clinicopathologic Features
Danielle Shitara, MD,
1Mauricio M. Nascimento, MD,
1Susana Puig, MD, PhD,
2Sérgio Yamada, MD,
1Milvia M. S. S. Enokihara, MD, PhD,
1,3Nilceo Michalany, MD,
1,3and Ediléia Bagatin, MD, PhD
1From the 1Department of Dermatology, Federal University of São Paulo, São Paulo, Brazil; 2Melanoma Unit, Dermatology Department, Hospital Clinic of Barcelona, IDIBAPS, Universitat de Barcelona, Barcelona, Spain and CIBER de Enfermedades Raras, Instituto de Salud Carlos III, Barcelona, Spain; and 3Department of Pathology, Federal University of São Paulo, São Paulo, Brazil.
Key Words: Nevus-associated melanomas; De novo melanoma; Breslow; Histologic subtype Am J Clin Pathol October 2014;142:485-491
DOI: 10.1309/AJCP4L5CJGKTJVDD
ABSTRACT
Objectives: The clinical significance of nevus-associated
melanoma compared with de novo melanomas remains controversial. It has been suggested that nevus-associated melanomas have a higher Breslow thickness and therefore worse prognosis. Over a 10-year period, this study evaluated the incidence of nevus-associated melanoma and its
prognostic significance related to clinicopathologic features.
Methods: Cross-sectional study from 1995 through 2004 in
a dermatopathology referral center. With available data, we evaluated sex, primary location, histologic subtype, Breslow thickness, Clark level, presence of ulceration, associated lesion, and histologic subtype of the associated lesion.
Results: Of 135,653 pathologic records from skin biopsy
specimens over a 10-year period, 1,190 melanoma records were selected. Nevus-associated melanomas corresponded to 390 (32.8%) melanomas, with thin melanomas having a nevus 1.52 times the association observed with thick melanomas (>1.01 mm; 95% confidence interval, 1.16-1.99;
P < .001). Superficial spreading melanoma was the most frequent, while no lentigo maligna melanoma was associated with nevi. The median Breslow thickness of nevus-associated melanomas was lower than that of de novo melanomas.
Conclusions: Nevus-associated melanomas, which
represent one-third of the melanomas in southeast Brazil, are associated with intermittent sun exposure, superficial spreading melanomas, and lower Breslow thickness. This is one of the largest series describing nevus-associated melanomas in Latin America.
The global incidence of melanoma has risen in the past 50 years, despite increasing awareness and public health campaigns.1,2 In the United States, the incidence rates have
risen from 13 per 100,000 in 1990 to 21 per 100,000 in 2006, corresponding to the sixth most frequently diagnosed cancer in men and seventh in women and one of the most frequently diagnosed cancers in youth.1 In southern Brazil,
there has also been an increase in the relative incidence of melanoma, 38% among men and 11% among women, between 1979 and 1987.3 According to the National Institute
of Cancer (Instituto Nacional do Câncer),4 3,170 new cases
of melanoma in men and 2,060 in women were expected in Brazil in 2012, especially in the southern region of Brazil, where the population of European descent is greater. The lack of a centralized melanoma case registry and of mandatory disease notification may account, among other factors, for the nonconformity of national and international data.5
Among the melanoma risk factors described in the literature, the presence of multiple melanocytic nevi (>100 nevi; relative risk [RR], 6.89; 95% confidence interval [CI], 4.63-10.25) and atypical melanocytic nevi (RR, 6.36; 95% CI, 3.80-10.33)6,7 stands out, but the influence of preexisting
pigmented lesions in melanoma genesis remains controversial. Considering epidemiologic and histologic studies, melanoma seems to arise either in association with a preexisting nevus or de novo, without any associated lesion.8
The described incidence of melanoma associated with a preexisting lesion may vary from 20% to 50%.9-16
The clinical significance of nevus-associated melanomas compared with de novo melanomas remains controversial. Some authors suggest that nevus-associated melanomas may have a higher Breslow thickness and therefore worse
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prognosis.12 Other authors13,14 have obtained different
results with a lower Breslow thickness for nevus-associated melanomas. There have been suggestions that the development of nevus-associated melanoma would increase the risk of having another nevus-associated melanoma by 9-fold.11
We aim to evaluate the incidence of nevus-associated melanoma and its association with clinical and pathologic features over a 10-year period.
Materials and Methods
This cross-sectional study was carried out in a dermatopathology center in São Paulo, Brazil. The study protocol was submitted and approved by research ethics committees of Universidade Federal de São Paulo/UNIFESP-EPM (number 188.713, January 24, 2013).
All data available in pathologic records from skin biopsy specimens over a 10-year period (1995-2004) from a dermatopathology referral center were evaluated, and only melanoma records were included in this study. All melanoma cases were evaluated by a single experienced dermatopathologist (N.M.) using previously described morphologic features.17-19 The following parameters available
in the melanoma pathologic records were considered for clinicopathologic correlation: sex, primary location, histologic subtype, Breslow thickness, Clark level, presence of ulceration, associated lesion, and histologic subtype of the associated lesion. Only data available in the pathologic records were included in the study. Regarding primary location, head and neck were grouped as “Head”; trunk and lumbar areas were grouped as “Trunk.” Histologic subtypes were classified as follows: superficial spreading melanoma (SSM), nodular melanoma (NM), lentigo maligna melanoma (LMM), acral lentiginous melanoma, and other (fusiform melanoma, desmoplastic melanoma, amelanotic melanoma, and melanoma metastasis). Since the distinction of melanoma cells and nevus cells, especially in nevoid melanomas, can be difficult and controversial, we chose not to include any of the nevoid melanoma cases in this study.20,21
Lesions located in the trunk and extremities were considered located in intermittent sun-exposed areas, while lesions in the head were considered located in chronic sun-exposed areas. Genital and acral lesions were considered non–sun-exposed areas.
Statistical Analysis
For each analyzed variable, only data available were considered valid. Associated nevus was described with percentages and 95% CIs. To estimate the relation of associated nevus with selected risk factors, we calculated prevalence ratios (PRs) and 95% CIs, with associated nevus
as a dependent variable and various exposure factors as independent variables.
Most independent variables were grouped into two or three categories. Variables selected in the univariate analysis at a .20 significance level were included in the multivariate analysis. PRs and their 95% CIs were estimated using a generalized linear model with binomial distribution and log link function.22
Statistical significance was assessed using the c2 test.
The Mann-Whitney test was used for comparing the Breslow thicknesses of de novo and nevus melanomas. A two-sided
P value of less than .05 was considered to indicate statistical
significance. All analyses were performed using STATA/SE 12.1 for Windows (StataCorp LP, College Station, TX).
Results
Of 135,653 pathologic records from skin biopsy specimens over a 10-year period (1995-2004), only the records with the diagnosis of melanoma were selected for the evaluation, totaling 1,190 melanoma records. Unfortunately, not all melanoma records presented all the parameters evaluated, with information missing in some cases. Therefore, only available data were considered valid for statistical analysis.
Melanomas were located mainly in trunk and extremities (424 [43.0%] of 985 and 305 [31.0%] of 985, respectively)
❚Table 1❚. The most common histologic subtype was SSM
(517 [62.3%] of 830) (Table 1). Most melanomas without any specified subtype corresponded to in situ melanomas (87.5%). Of all melanomas evaluated, 707 (61.1%) of 1,147 were invasive melanomas, of which 446 (63.1%) of 707 were thin melanomas (Table 1). LMM was significantly associated with chronic sun-exposed areas (P < .001), while SSM and NM were related to intermittent sun-exposed areas. Almost three-fourths of the melanomas (729 [74.0%] of 985) were located in intermittent sun-exposed areas.
Of the general melanoma sample, 390 (32.8%) of 1,190 (95% CI, 30.1%-35.5%) corresponded to nevus-associated melanomas. Regarding primary location, acral and head did not show any association with melanoma arising in a nevus (P = .706). Nevertheless, the trunk was significantly more likely to be associated with a nevus compared with the head (PR, 2.92; 95% CI, 2.15-3.97; P < .001; Table 1). No significant association was established between nevus-associated melanoma and sex (P = .548).
When considering sun-exposed areas and nevus association, melanomas in chronic sun-exposed areas were associated with a lower risk of preexisting nevus compared with melanomas in intermittent sun-exposed areas (Table 1). Of all histologic subtypes, SSM represented most cases of nevus-associated melanoma (P < .001;
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Table 1). After multivariate analysis, primary location and histologic subtype were the variables independently related to associated nevus (Table 1).
Of 390 nevus-associated melanomas, 243 (62.3%) were invasive melanomas ❚Image 1❚ and ❚Image 2❚. Applying the
Mann-Whitney test, the median Breslow thickness for de novo melanomas (0.85; interquartile range, 0.50-1.75) was greater than that for nevus-associated melanomas (0.70; interquartile range, 0.45-1.08; P < .001) ❚Table 2❚.
Discussion
Because of Brazil’s ethnic diversity, the most common histologic subtype of melanomas varies according to the region in question, with SSM being the most frequent histologic subtype among the central-southern populations. The melanoma samples for this study were collected in São Paulo, located in southeast Brazil, where the white population is predominant, mainly due to European immigration. Our
findings corroborate the international literature, in which SSM was the most common histologic subtype observed (517 [62.3%] of 830; Table 1), and the primary location was the trunk, followed by extremities.1,5,23
LMM was the histologic subtype most related to chronic sun-exposed areas (P < .001), while SSM and NM were related to intermittent sun-exposed areas, corroborating the idea suggested by Whiteman et al24 that LMM is widely
accepted to be caused by chronic sun exposure.25
The described nevus melanoma incidence may vary from 20% to 50% in the literature, considering clinical and epidemiologic studies. Regarding studies in which histologic evaluation of melanomas was conducted, benign nevus was found in association with 20.6% to 42% of melanomas, in agreement with the results obtained from this study (390 [32.8%] of 1,190 melanomas).12-14,26,27 The
variables that were statistically significant in association with nevus-associated melanomas in univariate analysis were primary location, histologic subtype, and Breslow thickness, but after multivariate analysis, the only variables
❚Table 1❚
Distribution of Melanoma Sample and Prevalence Ratio of Associated Lesions According to Clinical and Pathologic Variables
Nevus Absent, Nevus Present, Crude PR Adjusted PR
Variable No. (%) No. (%) P Value (95% CI) (95% CI)
Histologic subtype n = 589 n = 241 <.001 P < .001 P < .001 SSM 302 (51.3) 215 (89.2) 3.02 (2.08-4.38) 2.65 (1.61-4.35) LMMa 124 (21.0) 0 1.00 1.00 NM 113 (19.2) 21 (8.7) ALM 33 (5.6) 3 (1.3) Other 17 (2.9) 2 (0.8) Location n = 668 n = 317 <.001 P < .001 P = .008 Acral 49 (7.4) 10 (3.2) 1.00 1.00 Head 165 (24.7) 29 (9.1) Genitalb 1 (0.1) 2 (0.6) Extremities 219 (32.8) 86 (27.1) 1.83 (1.30-2.57) 1.27 (0.83-1.96) Trunk 234 (35.0) 190 (60.0) 2.92 (2.15-3.97) 1.70 (1.15-2.51) Solar exposure n = 668 n = 317 <.001 P < .001 No 50 (7.5) 12 (3.8) 1.00 Intermittent 453 (67.8) 276 (87.0) 1.95 (1.17-3.28) Chronic 165 (24.7) 29 (9.2) 0.77 (0.42-1.42) Breslow thickness n = 776 n = 382 .210 P < .001 In situ melanomas 312 (40.2) 139 (36.4) Invasive melanomas 464 (59.8) 243 (61.3) Thin (≤1 mm)c 267 (58.6) 179 (74.6) <.001 1.52 (1.16-1.99) Thick (>1 mm)c 189 (41.4) 61 (25.4) <.001 1.00 1.01-2.00 mm 98 (51.9) 49 (80.3) 2.01-4.00 mm 63 (33.3) 10 (16.4) >4.00 mm 28 (14.8) 2 (3.3) Sex n = 789 n = 388 .502 P = .548 Female 417 (52.9) 197 (51.0) 1.00 Male 372 (47.1) 191 (49.0%) 1.06 (0.88-1.27) Clark leveld n = 760 n = 381 <.001 P = .002 I 315 (41.4) 140 (36.7) 1.75 (1.19-2.58) II 146 (19.2) 79 (20.7) III 194 (25.5) 134 (35.2) IV 105 (13.8) 28 (7.3) 1.00
ALM, acral lentiginous melanoma; CI, confidence interval; LMM, lentigo maligna melanoma; NM, nodular melanoma; Other, fusiform melanoma, amelanotic melanoma, desmoplastic melanoma, and metastasis of melanoma; PR, prevalence ratio; SSM, superficial spreading melanoma;.
a For PR value, LMM cases were not taken into account.
b For PR value, the only three cases of genital melanoma were not taken into account.
c Eleven melanomas did not present a measurable Breslow thickness (8 in general melanoma sample and 3 in nevus-associated melanoma sample). d For PR value, Clark V cases were not taken into account.
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A B
C ❚Image 1❚ Nevus-associated melanoma. A, Melanoma
associated with a nevus showing melanoma cells in the epidermis and associated dermal nevus (H&E, ×100). B, Same lesion showing positivity of melanoma cells and negativity of nevus cells (immunohistochemistry HMB-45, ×200). C, Same lesion showing intense positivity of intraepidermal melanoma cells and weakly positive nevus cells (Melan A, ×100).
B A
❚Image 2❚ Nevus-associated melanoma. A, Melanoma on the left side with large epithelioid atypical cells and nevus on the right side in dermis with small nonatypical cells (H&E, ×100). B, Detail of melanoma and nevus collision area (H&E, ×200).
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that remained independently associated with nevus-associated melanoma were primary location (P = .008) and histologic subtype (P < .001; Table 1).
When considering the anatomic distribution of nevus-associated melanomas, most melanomas were located on intermittent sun-exposed areas (trunk and extremities; Table 1).13,28 The finding that the trunk is the most frequent primary
location is in agreement with previous studies,12,13 being 2.92
times more likely to be associated with a nevus-associated melanoma than other locations (95% CI, 2.15-3.97; P < .001; Table 1). What stands out is that acral and head did not show any association with nevi in the majority of melanomas (49 [83.1%] of 59 and 165 [85.1%] of 194, respectively; Table 1). It has been suggested that this difference is unlikely to be due to the anatomic distribution of nevi, because nevus density, as a function of surface area, has been reported to be higher on the face than on the trunk.13
Of all histologic subtypes, the association of a nevus with SSM was 3.02 times the association observed with other histologic subtypes (95% CI, 2.08-4.38; P < .001; Table 1). It has been suggested that histologic subtype rather than thickness seems to be the primary factor, with SSM more likely to arise in a nevus than other types of melanoma.13,29
Indeed, some authors found that NM was less related to nevus even after controlling for Breslow thickness.29 In
addition, no LMM was related to nevus, despite being the melanoma subtype characterized by slow horizontal spreading along the basal cell layer,19 corroborating previous
findings that it corresponds to the histologic subtype least likely to be associated with a nevus (Table 1).13,16,30 This
may partially be due to the fact that LMM shows distinct clinical and epidemiologic characteristics and may arise from a different pathogenic pathway than does nevus-associated melanoma.13,31 LMM is more frequent in chronically
sun-damaged areas, while nevus-associated melanomas would be more frequent in intermittent sun-exposed areas.24,25 It
has been suggested that there may be different pathways in melanoma genesis and that one determinant of melanoma development would be the propensity of the host to develop nevi.13,24,28,31-33 In the first pathway, melanocytes in
nevus-prone individuals would require modest amounts of sunlight only in the early stages of tumorigenesis, with host factors
driving tumor progression thereafter, and in another pathway, melanocytes of people with a low propensity to develop nevi would require long-term accumulation of sun exposure for melanoma to develop. In the latter pathway, melanomas would increase with age and affect the chronically sun-exposed skin of the head and neck, face, and distal and dorsal extremities, with the surrounding skin typically showing marked solar elastosis and typically not in association with a precursor melanocytic nevus or in patients with numerous melanocytic nevi. Microscopically, these melanomas show a radial growth phase comprising melanocytes arranged as solitary units with poor lateral circumscription. On the other hand, the nevus-related pathway would affect younger patients, decreasing with older age, arising primarily on the intermittently sun-exposed skin of the trunk and proximal extremities on individuals with multiple melanocytic nevi. Microscopically, these melanomas are composed of larger melanocytes that are arranged primarily in nests and display upward intraepidermal scatter in their radial growth phase. Our findings that nevus-associated melanomas were more frequent on the trunk and extremities, in intermittent sun-exposed areas (P < .001), and of the SSM subtype, while most melanomas located on the head were not associated with a nevus and no LMM was found in association with a nevus, corroborate previous findings that there may be more than one pathway to melanoma genesis.
Roughly two-thirds of nevus-associated melanomas corresponded to invasive melanomas. Comparing thin and thick melanomas, thin melanomas were significantly associated with a nevus (PR, 1.52; 95% CI, 1.16-1.99;
P < .001), in agreement with previous publications,14,34
even though this parameter did not remain significant after multivariate analysis. The greater incidence of nevus-associated melanoma in thin melanomas may be justified partially by the fact that melanoma progression destroys nevus cells, so early diagnosis may increase the chance of finding melanoma with associated nevus.30,35 Nevertheless,
other authors did not find an association of an eclipsing of nevus cells by growing melanomas.36
The distribution of nevus subtypes observed in this study is pursuant to the findings of Marks et al,30 in that more
than half of nevi associated with melanoma were common acquired nevi ❚Table 3❚. Nevertheless, we found a smaller
percentage of atypical (or dysplastic) nevi. This difference may be explained by the lack of consensus regarding the diagnosis of atypical nevi in the literature.16,37-40
The prognostic significance of nevus-associated melanoma remains controversial in the literature. In a prospective study, Weatherhead et al12 suggested that nevus-associated melanoma
had a higher Breslow thickness and therefore a worse prognosis compared with de novo melanomas. However, Garcia-Cruz et al35 could not demonstrate a significant difference between ❚Table 2❚
Median Breslow Thickness Related to Presence or Absence of Associated Nevus
Associated Nevus Breslow Thickness, mm Yes No
Median 0.70 0.85 Interquartile range 0.45-1.08 0.50-1.75 Minimum-maximum 0.25-8.00 0.20-15.00 No. of observations 240 456 by guest on June 3, 2016 http://ajcp.oxfordjournals.org/ Downloaded from
the prognosis of nevus-associated and de novo melanomas. Kaddu et al,14 after evaluation of 667 nevus-associated
melanomas and 519 de novo control melanomas, found lower Breslow thickness and a 5-year survival rate of 93.5% for nevus-associated melanomas, even though the latter did not show statistical significance. Purdue et al13 also obtained a
lower Breslow thickness for nevus-associated melanomas. The present study corroborates the findings of Kaddu et al14 and Purdue et al.13 The median Breslow thickness of
nevus-associated melanomas was lower than that of de novo melanomas (Table 2), suggesting a more favorable prognosis based on the Breslow thickness of the primary melanoma,3,41,42
although a 5-year survival assessment was not possible in this study due to the follow-up data being unavailable.
This is one of the largest series describing melanomas associated with nevus described in Latin America. Melanoma arising in a nevus represents one-third of the melanomas in southeast Brazil, being associated with thin, superficial spreading melanomas, located mainly on the trunk, corroborating the data in the international literature.13,14
Address reprint requests to Dr Shitara: Dept of Dermatology, Federal University of São Paulo, São Paulo, Brazil, R Borges Lagoa, 504 zip 04038-001, São Paulo-SP, Brazil; danielleshitara@yahoo.com.br.
The research was funded by grants from FAPESP (São Paulo Research Foundation/Fundação de Amparo à Pesquisa do Estado de São Paulo), process number 2012-15238-0. The sponsors had no role in the design and conduct of the study; the sponsors also had no role in the collection, analysis, and interpretation of data.
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❚Table 3❚
Subtypes of Associated Lesions
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Junctional nevus 79 (20.2) 51 (13.1) Compound nevus 72 (18.4) 37 (9.5) Intradermal nevus 37 (9.5) 1 (0.4) Congenital nevus 6 (1.5) Not specified 94 (24.1) 13 (3.3) by guest on June 3, 2016 http://ajcp.oxfordjournals.org/ Downloaded from
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