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§
From the Departments of Surgery*
and Clinical
Pathology,§
Kuopio University Hospital, Kuopio;
and the Departments of Anatomy
and
Pathology and Forensic Medicine,
University of
Kuopio, Kuopio, Finland
| Abstract |
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| Introduction |
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, have become available it is even more important to
identify the patients at high risk of developing metastatic
disease.5
More research is also needed to improve our
basic understanding on the biology of cutaneous melanoma. CD44 is a structurally variable and multifunctional cell surface glycoprotein expressed on most cell types.6,7 Many functions of CD44 are mediated through interaction with its ligand hyaluronan (HA),8 a ubiquitous extracellular polysaccharide.9 HA is abundant in soft connective tissues, but also in epithelial and neural tissues.8 HA organizes certain proteoglycans in the extracellular matrix, and facilitates cell migration and proliferation during embryogenesis, inflammation, and wound healing.8-11
The interaction of CD44 with HA contributes to tumor cell proliferation,8,12 migration,6,8,13-15 invasion,6,8,16 and formation of metastatic tumor emboli or peritoneal implants.8,17-21 Previous experimental data suggest that CD44 and HA enhance growth and metastatic capacity of melanoma cells,17,18,21-26 but the clinical significance of this suggestion has not been confirmed in the relatively small and divergent clinical materials reported so far.27-35 We demonstrate here that the reduced stainings of cell surface CD44 and tumor cell associated HA are associated with each other, and with progressive disease and poor prognosis in localized cutaneous melanoma.
| Materials and Methods |
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This retrospective study consists of primary melanomas derived
from a consecutive series 369 clinical stage I cutaneous melanoma
patients with sufficient clinicopathological and long-term follow-up
data.36
The patients were diagnosed and treated in the
district of Kuopio University Hospital between 1974 and 1989. The
histological diagnosis, Breslow thickness and Clark level were
re-examined from 1 to 4 original sections of the primary tumor by the
same pathologist (VMK), unaware of the clinical data. Of the original
369 cases, 292 had enough archival tumor material available for the
present study (Table 1)
. The most
representative block was cut into new 5-µm-thick consecutive sections
for CD44 and HA stainings. Depending on the availability of
representative tumor material as compared with the original sections,
282 stainings with an antibody recognizing all forms of CD44 and 277
stainings for HA were eventually evaluable.
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CD44 was demonstrated by using a mouse IgG anti-CD44H antibody (clone 2C5) (R&D Systems, Abingdon, UK) which recognizes all forms of CD44.37 Adjacent 5-µm sections from tumors were deparaffinized and rehydrated using xylene and graded alcohols. The sections were microwaved in a 0.01 mol/L citrate buffer (pH 6.0) for 3 x 5 minutes, incubated in a citrate buffer for 18 minutes, and washed twice for 5 minutes with phosphate-buffered saline (PBS). Endogenous peroxidase activity was blocked by 5% hydrogen peroxide for 5 minutes, followed by a wash twice for 5 minutes with PBS. The sections were incubated with 1% bovine serum albumin (BSA) and PBS for 30 minutes at 37°C. The primary antibody was diluted with 1% BSA to 1:2000 and incubated on the slides overnight at 4°C. After another washing step, the bound antibody was localized using a biotinylated secondary antibody and an avidin-biotin-peroxidase detection kit (Vectastain ABC Elite Kit, Vector Laboratories, Burlingame, CA), and the slides were developed with diaminobenzidine tetrahydrochloride (DAB) (Sigma, St. Louis, MO), counterstained with Mayers hematoxylin, dehydrated, cleared and mounted with DePex (BDH Poole, UK). In each batch, a melanoma specimen processed without primary antibodies served as a negative control, and one CD44-positive melanoma block served as a source for positive control sections. In addition, the adjacent normal epidermis within the tumor served as positive internal control.
Preparation of bHABC and Staining of HA
The biotinylated complex of hyaluronan binding region and link protein (bHABC) was prepared from bovine articular cartilage as described previously.38,39 Briefly, the proteoglycans were extracted from the cartilage with 4 mol/L guanidinium chloride. The extract was dialyzed against distilled water in the presence of high molecular weight hyaluronan. The C-terminus of the proteoglycan molecule was cleaved off with trypsin, and the resultant complex of hyaluronan binding region and link protein (HABC) with HA was purified using hydroxylapatite chromatography and gel filtration. The complex was biotinylated, and the bHABC was separated from HA using gel filtration under dissociative conditions. The purity of the preparation was tested by polyacrylamide gel electrophoresis and Western blotting.
The sections were deparaffinized in xylene, rehydrated with graded
alcohols and washed with PB. Endogenous peroxidase was blocked with 1%
hydrogen peroxide for 5 minutes and nonspecific binding was blocked
with 1% BSA in PB for 30 minutes. The sections were incubated in bHABC
(2.5 µg/ml, diluted in 1% BSA) overnight at 4°C. The slides were
washed with PB and treated with avidin-biotin-peroxidase kit (1:200
dilution) for 1 h at room temperature. Following wash with PB the
color was developed with 0.05% DAB and 0.03% hydrogen peroxide in PB
at room temperature. The slides were counterstained with Mayers
hematoxylin for 2 minutes, washed, dehydrated, and mounted in Depex.
The specificity of the staining was controlled by digesting some
sections with 100 TRU/ml of Streptomyces hyaluronidase
(Seikagaku Kogyo Co., Tokyo, Japan) in the presence of protease
inhibitors before the staining, or preincubating the bHABC-probe with
hyaluronan oligosaccharides to block the specific binding site (Figure 1A)
.39
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Throughout the evaluations, the observers were unaware of the
clinical data. In all stainings, scoring was performed with a dual head
microscope (field diameter 490 µm) by two observers (JMK and VMK) in
the whole tumor area on the slide. In both CD44 and HA stainings, the
positivities were assessed qualitatively, ie, the tumor cells were
considered as positive when there was a homogeneous and clearly visible
signal present, and negative if the signal was absent. According to
this principle, the fraction of positively stained cancer cells in the
entire slide was evaluated within each specimen. The frequency
distribution and percentiles for the HA- and CD44-positive cancer cell
fractions within each specimen were analyzed within the whole series
(Figure 2)
. For both stainings, the
tumors were eventually categorized as high (91 to 100% of positively
stained cancer cells for CD44 and 71 to 100% of positively stained
cancer cells for HA) or reduced (0 to 90% of positively stained cancer
cells for CD44 and 0 to 70% of positively stained cancer cells for HA)
expressors according to the median percentage of positively stained
cancer cells.40
The staining intensity of hyaluronan in
the intratumoral stroma was compared qualitatively to the adjacent
normal HA-positive epidermis and categorized as follows: +, weaker than
epidermis; ++, as strong as epidermis; and +++, stronger than
epidermis.
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The SPSS-Win 7.5 program package was used in a PC computer for
basic statistical calculations. The
2
test was
used to compare the frequency distributions of clinicopathological
features between the original database (n = 369)
and the population available for the current study. A Spearman
correlation coefficient was used to test the relationships between
continuous variables. Nonparametric tests (Kruskal-Wallis) were applied
for the comparisons of staining levels between different
clinicopathological categories. Frequency tables were analyzed using a
2-sided Fishers exact test. In univariate survival analyses the EGRET
statistical software package was used for calculation of Kaplan-Meier
estimates of survival rates and the log rank analysis41
to
test the differences between the survival curves. Coxs multivariate
survival analysis was done using the Log likelihood ratio significance
test in a forward stepwise manner.42
The adequacy of the
proportional hazards assumption was tested by logminlog plots.
Overall survival (OS) analysis included as an event only the deaths due
to malignant melanoma. Deaths due to postoperative complications within
30 days were excluded. Recurrence-free survival (RFS) was defined as
the time elapsed between the primary treatment and the recurrent
melanoma. For all statistical tests, probability values less than 0.05
were regarded as significant.
| Results |
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The frequency distributions of the clinicopathological
characteristics, as well as the follow-up and survival times between
the original database (N = 369)36
and the patients with valid material available for CD44 and HA
stainings were almost identical (Table 1)
. The mean follow-up time of
all 292 patients was 6.3 ± 3.3 (SD) years (median, 5.4 years;
range, 0.518 years).
Staining Patterns of CD44 and HA
The CD44 positivity (median value 90%) was confined to tumor cell
membranes (Figure 1B)
. Most tumors showed intense membranous and
cytoplasmic HA-positivity (median value 70%), as did the consistently
positive epidermis (Figure 1C)
. The dermal stroma within and outside
the tumor was always HA positive (Figure 1A)
. The histograms of the
cellular CD44 and HA levels are shown in Figure 2
and the cellular CD44
and HA levels and stromal HA intensity in different categories in Table 2
.
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CD44 positivity was strongly associated with cellular HA according
to Spearmans statistics (r = 0.309;
P < 0.00005; N = 267) and a 2-sided
Fishers exact test (P = 0.005). Decreasing
levels of cancer cell-associated CD44 (Figure 1D)
and HA (Figure 1E)
were both related to increasing Breslow thickness
(
2
= 20.5, P < 0.00005 for
CD44 and
2
= 16.4, P = 0.001
for HA), increasing Clark level (
2
= 35.1,
P < 0.00005 for CD44 and
2
=
26.5, P < 0.00005 for HA), and increasing pT category
(
2=34.8, P < 0.00005 for CD44
and
2=19.1, P < 0.00005 for
HA), and this trend was evenly distributed within Breslows thickness,
Clarks level and pT categories. Decreasing CD44 and HA levels also
associated with bleeding (
2
= 7.4,
P = 0.024 for CD44 and
2
=
9.0, P = 0.011 for HA) and with recurrent disease
(
2
= 18.2, P < 0.00005 for
CD44 and
2=6.7, P = 0.01 for
HA). Stromal HA intensity did not show statistically significant
correlation with CD44 level or with any of the clinicopathological
variables.
Univariate Survival Analysis
During the follow-up, 84/292 patients (29%) had a recurrence, 52 patients (18%) died of melanoma, and 40 patients (14%) died of other causes. The 5-year rates for crude, overall, and recurrence-free survivals were 78%, 86%, and 75%, respectively.
Reduced levels of CD44 (0 to 90% positively stained cancer cells) and
cancer cell-associated HA (0 to 70% positively stained cancer cells)
predicted short OS (P = 0.0077 and
P = 0.0146, Figure 3
) and
short RFS (P = 0.0001 and P =
0.0141, Figure 4
) (Table 3)
. Reduced CD44 level predicted poor RFS
also within the low-risk (
1.5 mm) subgroup, (P
= 0.0147, N = 127, other data not shown). Stromal HA
intensity was not significantly related to OS or RFS. The conventional
parameters predicting poor RFS and OS were high tumor thickness and
high pT category (P < 0.00005 for both RFS and
OS, respectively), high Clarks level of invasion
(P < 0.00005 for RFS and P =
0.0001 for OS), bleeding (P = 0.0001 for both
RFS and OS) and male gender (P = 0.0292 for RFS
and P = 0.0339 for OS) (Table 3)
. In addition, the
reduction of CD44 and HA staining associated fairly well with
unfavorable prognosis also by using the 33rd and 66th percentiles of
frequency distribution as cut off points (RFS: P =
0.0027 for HA and P = 0.001 for CD44; OS:
P = 0.0632 for HA and P = 0.0112 for
CD44, other data not shown).
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Coxs multivariate analysis of 251 patients with a complete set
of data included variables that significantly predicted univariate
survival, except pT category because it includes Clarks level and
tumor thickness. Tumor thickness (P = 0.0008)
and bleeding (P = 0.0411) were associated with
short OS. Reduced CD44 level was an independent predictor of short RFS
(P = 0.0308). Other independent predictors of
short RFS were tumor thickness (P = 0.001) and
bleeding (P = 0.0346) (Table 4)
.
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| Discussion |
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There are no presettled criteria for selecting the cut off points for CD44 and HA positivities in cutaneous melanoma. We chose the median values, because they can be used without introducing a statistical bias,40 and because they easily divided the material into two groups of equivalent size. Dichotomizing continuous variables according to a single more or less arbitrary percentile may discard important relationships. However, using the 33rd and 66th percentiles of frequency distribution as HA and CD44 positivity cut off points separated the present series into significantly different prognostic groups almost as effectively as the median (data not shown), thus strengthening our results. The conventional parameters that predicted poor RFS and OS in this series have also been established in most prognostic studies worldwide,3,43-45 indicating that the current material was comparable with previous ones. Thus, we believe that the present findings significantly contribute to the current understanding in this area.
The present results on clinical tumors apparently contrast with those of previous experimental studies, in which the growth or metastatic capacity of melanoma cells is inhibited by breaking the CD44-HA interaction with CD44 antibodies,23 soluble IgG fusion proteins22 or hyaluronan oligomers.26 Considering that cutaneous melanomas evolve in basal epidermis, surrounded by keratinocytes with high levels of CD4446,47 and an environment rich in HA,47 results on CD44 and HA metabolism in melanoma cell lines may not be comparable to the clinical behavior of human melanoma. The genetically labile and heterogeneous nature of cells within a single tumor and between tumors may further lead to selection of cell lines that do not represent the expression pattern in vivo.48,49
Both high50-52 and reduced53-55 CD44 expression levels have been associated with cancer growth and adverse prognosis in various malignant tumors, supporting the concept that the growth regulation of cancer cells by CD44 is highly dependent on the cellular background.53,56 Supporting our findings, CD44 expression diminished with increasing invasiveness of primary tumors30,31,34 and in metastatic melanomas.33 However, in the only prognostic study concerning CD44 expression in cutaneous melanoma, high CD44 level in primary malignant melanomas (n = 92) associated with progressive disease and poor univariate survival.32
Although elevated concentrations of HA have been found in several human cancers,8,57 there are relatively few studies in which HA has been detected in specific locations of the cancer tissue architecture.58-63 Two categories have arisen among the malignancies studied with this kind of assay. In one of them, comprising malignancies of hyaluronan-poor monolayered epithelia such as that of colon,58 breast59 and ovary,60 abnormally increased hyaluronan is strongly associated with unfavorable prognosis. The other category with normally hyaluronan positive squamous epithelia, like that in the esophageal,61 laryngeal62 and lung63 carcinoma, show an opposite trend where loss of cell surface HA is associated with poor differentiation,61,63 metastasis and poor survival.62 The present study indicates that cutaneous melanoma also belongs to the latter category.
The mechanism by which CD44 (and HA) influence the clinical outcome of cutaneous melanoma patients in the present series remains to be solved. In vitro, hypoxia leads to down-regulation of CD44 and subsequent melanoma cell detachment, which, on reoxygenation, is followed by up-regulation of CD44, cell reattachment, and growth.64 Melanoma cells may thus modulate their CD44/HA function to enable initial cell detachment (down-regulation)64 and later formation of metastatic deposits (up-regulation),6,21-23 depending on environmental factors such as oxygen content.64 Cell surface CD44 and HA maintain adhesive restraints between the cells in normal epidermis,46,47,65,66 and may mediate a tumor suppressive effect also in primary cutaneous melanoma by the same mechanism. It should be noticed that the metastasis suppression by the standard CD44 isoform can be independent of its ability to bind to hyaluronate and may require also other ligands.67 In addition, cell surface CD44, with its ligand HA, may suffer as victims of enhanced proteolysis, and diffuse out of the tissue or be subjects of premature endocytosis and degradation, as discussed earlier.62
Restoration of CD44H expression in colon carcinomas has been observed to reduce tumorigenicity in vitro and in vivo.68 Because of the possibility that the biological role of CD44 may change depending on the cellular environment, the use of CD44 in gene transfection treatments might be complicated in melanoma. Defining how the malignant cells regulate their CD44 expression and its affinity for HA or other ligands could provide alternative ways to interfere with tumor cell spreading. Meanwhile, quantification of CD44 in the primary cutaneous melanoma offers a reproducible and available prognostic tool for clinical practice, for instance to select patients for more aggressive therapy.
| Acknowledgements |
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| Footnotes |
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Supported by grants from the Cancer Fund of North Savo (Savon Syöpärahasto), The Paavo Koistinen Foundation, The Finnish Cancer Foundation, The Finnish Medical Society Duodecim, and by Special Government Funding of Kuopio University Hospital, Kuopio, Finland.
Accepted for publication June 14, 2000.
| References |
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-2b in melanoma. Semin Oncol 1997, 24:(Suppl 4):S1623
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