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Molecular Oncology, Markers, Clinical Correlates |
Academic Medical Center, Department of Pathology, 1105 AZ Amsterdam, the Netherlands [M. M. E., J. J. K., P. D., K. C. K., G. J. A. O.], and Johns Hopkins Hospital, Department of Gastroenterology, Baltimore, Maryland 21205 [F. M. G.]
| ABSTRACT |
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Using a nationwide pathology report database system, we identified patients with the MTS phenotype. SGCs from 10 MTS patients and the colorectal carcinomas from 3 additional MTS patients were collected. In addition, SGCs from eight patients without a history of visceral neoplasm were collected. MSI was detected in 9 of 13 MTS-associated tumors (69%) versus 0 of 8 sporadic SGCs (P = 0.002). Except for the age of onset of colorectal carcinoma [58 years in the MSI-positive group versus 69.8 years in the MSI-negative group (P = 0.17)], no differences were seen between the MSI-negative and the MSI-positive MTS patients. Loss of expression of hMLH-1 (n = 4) or hMSH-2 (n = 4) was found in MSI-positive patients only.
MSI and loss of expression of MMR genes can be used as markers for MTS in patients with SGC. Consequently, MSI and loss of MMR gene expression in a patient presenting with SGC as the initial malignancy have important consequences for the patient and family. There are at least two variants of MTS with different molecular genetic mechanisms because 31% of the patients with the MTS phenotype had no MSI.
| INTRODUCTION |
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MTS is defined as the presence of: (a) a sebaceous gland
adenoma, epithelioma, or carcinoma; and (b) an internal
malignancy. Internal malignancies that are most often seen in MTS
patients are CRCs and genitourinary tract neoplasms predominantly
originating from the bladder, uterus, renal pelvis, or ovaries, which
together account for
75% of the observed internal malignancies in
MTS. Furthermore, breast, hematological, head and neck, and small
intestinal malignancies have been described in combination with
sebaceous gland tumors (3
, 4)
. Also, the diagnosis MTS is
appropriate for a patient with multiple KAs in combination with more
than one visceral malignancy and a positive family history of the MTS
(4)
. Because a subset of patients fulfilling these
criteria appeared to have HNPCC, a relation between HNPCC and MTS was
first suggested by Lynch in 1981 (5)
.
HNPCC (Lynch syndrome) is characterized by an autosomal dominantly
inherited predisposition to the development of CRC or specific
extracolonic cancers, such as endometrial or gastric carcinomas. CRCs
in HNPCC patients present at a young age (
44 years) and have a
favorable prognosis compared to sporadic malignancies. HNPCC can be
diagnosed on clinical grounds if all three Amsterdam criteria are
fulfilled: (a) three or more relatives with histologically
verified CRC, one of whom is a first degree relative of the other two;
(b) CRC involving at least two generations; and
(c) one or more CRC cases diagnosed before age 50
(6)
.
HNPCC is caused by an inherited germ-line mutation in one allele of MMR genes. When a somatic loss-of-function alteration of the remaining wild-type allele occurs, MMR deficiency develops. The MMR system repairs small errors in repeat sequences of the DNA (microsatellites), which occur during replication. Consequently, MMR deficiency results in accumulating mutations of these microsatellites, which is termed MSI. Carcinomas of HNPCC patients show MSI (7) . Presently, defects in six genes have been described leading to the HNPCC phenotype: hMLH1, hMSH2, hPMS1, hPMS2, hMSH6, and the transforming growth factor ß type II receptor gene (8, 9, 10) . Molecular genetic studies in MTS patients have shown MSI in both sebaceous gland tumors and CRC (11 , 12) . Also, MSI in KAs and actinic keratoses from MTS patients has been described (13, 14, 15) . In contrast, the degree of MSI in sporadic KAs and other skin tumors, such as basal cell carcinomas, squamous cell carcinomas, melanomas, actinic keratoses, and Bowens disease is very low, although no data for sporadic sebaceous gland tumors are available (13, 14, 15, 16) . In addition, germ-line mutations in the MMR genes hMSH-2 and hMLH-1 have been described in MTS patients, further indicating that MTS might be an expression variant of HNPCC (17, 18, 19) .
MTS is phenotypically distinguished from HNPCC by the presence of sebaceous gland tumors and/or KAs in patients with MTS. In MTS, 30% of the sebaceous gland tumors are SGCs. SGCs account for a minority of the skin cancers in the general population and are rarely diagnosed. In most cases, SGCs are seen in the eyelid, but they can develop in any sebaceous gland in the body; the head and neck region is the most frequently affected part of the skin (20) . SGCs usually occur in patients aged 6080 years. In about 41% of MTS patients, a sebaceous gland tumor presented as the first malignancy before or concurrent with an internal malignancy. Because MTS patients are often prone to multiple internal malignancies, as many as 63% of the MTS patients with a sebaceous gland tumor have a concurrent internal cancer or will develop an additional (internal) neoplasm (3) . These data emphasize the importance of complete evaluation and close follow-up for gastrointestinal and genitourinary cancer in a patient with a sebaceous gland tumor when the diagnosis MTS is considered.
In 1996, a 61-year-old man with a SGC on the back ("index patient") presented to our institution for evaluation. Investigation revealed that this patient had a history of intestinal malignancies. This index patient prompted us to address whether MSI can distinguish between patients with SGC as part of MTS and patients with sporadic SGC. In addition, IHC for the expression of proteins encoded by the MMR genes hMLH-1 and hMSH-2 was evaluated as a potential marker to distinguish between MTS and sporadic SGC.
| MATERIALS AND METHODS |
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Remaining Study Subjects.
Additional cases with SGC were identified by searching the surgical
pathology files from 1984 to 1997. Eight patients with SGCs were found.
None of them had a history of intestinal or other visceral carcinomas.
This group was considered to have sporadic SGC. Then, a nationwide
search was done for patients with SGC and a history of one or more
gastrointestinal carcinomas (fulfilling the criteria for MTS) using the
PALGA system, a computerized database system of all pathology
reports in the Netherlands. The PALGA system has nationwide coverage
since 1992 and is considered complete. Pathology reports of 12 patients
with a history of both intestinal tumors and SGCs, from whom tissue was
available, were identified. Paraffin-embedded tissue from both SGC and
CRC of three of these patients, tissue from only SGC of six of these
patients, and tissue from only CRC of the three remaining patients were
obtained. All tumors were reexamined by an experienced pathologist at
our institution. Besides the date of birth, gender, and the date of the
pathology report, no clinical data were available.
Tissue and DNA Preparation.
Unstained sections of 5 µm were cut from paraffin-embedded tumor
samples and microdissected. The microdissected tumorous tissue
contained at least 75% neoplastic cells and was put in an Eppendorf
tube containing proteinase K solution [100 µg/ml proteinase K, 50
mM Tris (pH 8.5), 0.2% Tween 20, 1 mM EDTA]
to degenerate the proteins in the tissue. The samples were incubated
overnight at 56°C and proteinase K was inactivated by heating the
solution at 96°C for 10 min. This solution was used as a stock for
PCR reactions.
MSI Analysis.
MSI was analyzed using PCR markers as recently described by the
Bethesda working group on HNPCC (21
, 22)
. We used as
primers BAT-25, BAT-26, BAT-40, D2S123, and D17S250. PCR was performed
in 10-µl reactions using 2550 ng of DNA, 13 mM
MgCl2, 175 µM dNTPs, and 5
pM of each primer. The forward primer was end-labeled with
[
-32P]ATP and 0.5 units of AmpliTaq Gold
polymerase (Perkin-Elmer). Amplification consisted of 33 cycles (95°C
for 30 s, 55°C for 60 s, 72°C for 2 min) after an initial
step of 9 min at 95°C. After PCR, the samples were mixed with loading
buffer (95% formamide, 20 mM EDTA, 0.05% bromphenol blue,
0.05% xylene cyanol), heat-denatured, and run on a 6% polyacrylamide,
7 M urea gel for 23 h at 2 kV. After the run, gels were
vacuum-dried and autoradiographed overnight. Tumor samples were scored
as unstable for a marker when new alleles were seen compared to
the wild-type sample. Tumors were defined as MSI-positive if more than
one marker showed shifts in length when compared with normal tissue
(21
, 22) .
IHC for hMLH-1 and hMSH-2.
Unstained 5-µm sections of the paraffin-embedded samples of the SGCs
(n = 18) and CRCs (n = 3) were cut.
Sections were dewaxed and rehydrated in xylene and a series of graded
alcohol. Endogenous peroxidase activity was blocked in 0.3%
H2O2 in methanol for 20
min. Slides were submerged in citrate buffer (0.01
M; pH 6.0) and heated in a
temperature-probe-controlled microwave oven for 10 min at 100°C.
After cooling for 20 min, 10% normal goat serum in PBS was applied for
20 min. The sections were subsequently incubated for 1 h at 37°C
with the primary antibodies. A monoclonal mouse antihuman hMLH-1
(PharMingen International, CA) was used at a dilution of 1:20 in
PBS. A monoclonal mouse antihuman hMSH-2 (Calbiochem, CA) was
used at a dilution of 1:100 in PBS. After washing, biotinylated goat
antipolyvalent antibody (Lab Vision Corporation, CA) in PBS
(1:1) was applied for 15 min, followed by streptavidin peroxidase in
PBS (1:1) for 15 min. The peroxidase activity was visualized using
3,3'-diaminobenzidine (1:20) in Tris-HCl, 0.05 M,
with 0.1% H2O2 for 10 min.
Counterstaining of the nuclei was done with hematoxylin. Adjacent
normal tissue in each sample served as the positive control. The
primary antibody was replaced by PBS as the negative control.
Stained slides were evaluated for the presence of expression of hMLH-1 or hMSH-2 in the tumor by two independent observers (G. J. A. O. and J. J. K.).
Statistics.
Comparisons between groups were statistically evaluated using the
Fishers exact test or Mann-Whitney U test, whichever was
appropriate.
| RESULTS |
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In the MTS group, MSI was present in samples of 9 of 13 patients
(69%). The average age of onset of the first malignancy in these nine
patients was 57.7 years (range, 3674). Samples from four patients
(31%) did not show MSI. In the MSI-negative group, the average age of
onset of the first malignancy was 59.0 years (range, 3477) and that
of SGC was 68 years (range, 5977; Table 2
). The average age of onset
of gastrointestinal carcinoma in the MSI-positive group was 58 years
(range, 3676) compared to 69.8 years (range, 6080) in the
MSI-negative MTS patients (P = 0.17). In all four
patients (patients 9, 12, 18, and 21) from whom SGC and CRC tissue was
available, both tissue types showed a concordant MSI status. In the
index case, all carcinomas showed MSI. In the sporadic SGCs, none of
the samples showed MSI for any of the markers. The difference in MSI
status between the MTS and sporadic groups was statistically
significant (P = 0.002; Fishers exact test). When MSI
was present (Fig. 1)
, BAT-40, BAT-26, and
BAT-25 showed shifts in all samples (n = 9), marker
D17S250 showed shifts in seven samples, and marker D2S123 showed shifts
in eight samples.
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| DISCUSSION |
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MSI is a phenotypic feature of HNPCC-associated tumors, and it has been
described in MTS malignancies (11
, 12)
. MSI occurs
infrequently in most sporadic carcinomas, including skin cancer
(7
, 13, 14, 15, 16)
. However, no MSI data for sporadic SGC are
available. In our study, sporadic SGC did not show MSI. In contrast,
malignancies from 9 of 13 (69%) MTS patients showed MSI. In patients
with both CRC and SGC available, a 100% concordance in MSI status was
noted. Thus, the sensitivity of MSI as a marker for MTS in SGC patients
was 69%, and the specificity was 100%. Of note, absence of MSI was
found in 31% of MTS patients, indicating that another molecular
genetic mechanism might lead to the MTS phenotype. This could either be
a MMR-related pathway, which does not exhibit MSI, as was recently
described in tumors of patients with a germ-line hMSH-6 mutation
(23)
, or a MMR-independent pathway. Because SGCs are very
rare (
0.2% of all skin malignancies are SGCs; Ref.
24
), a coincidental occurrence with CRC in all
MSI-negative MTS cases appears unlikely, although this possibility
cannot be completely excluded.
Our results are in agreement with Honchel et al. (11) , who reported MSI in 46% of carcinomas of MTS patients (compared to 69% in our study). These investigators also found longer survival, earlier age of onset of visceral malignancies, and higher numbers of internal malignancies in MSI-positive patients compared to the MSI-negative group. Based on clinical and genetic differences, Honchel et al. (11) suggested different subgroups of MTS patients, a concept supported by our data. The data points to two variants of MTS: one sharing its pathophysiology and genetic cause with HNPCC, characterized by early age CRC and a strong family history of at least CRC; and a second, MSI-negative variant of MTS, with late onset cancer and a less pronounced family history. The molecular mechanism underlying the latter variant has still to be determined. In the study of Kruse et al. (17) , MSI was found in all MTS patients, suggesting a 100% correlation between MTS and HNPCC. The 69% rate of MSI in our study could be related to different patient selection methods.
The association between HNPCC and MTS has been confirmed by studies showing germ-line mutations in the MMR genes, hMLH-1 and hMSH-2, in MTS patients. In our study, MSI-positive patients had loss of expression of hMLH-1 (n = 4) or hMSH-2 (n = 4), whereas all MSI-negative and sporadic SGC showed full expression of both. In one MSI-positive tumor sample, IHC was inconclusive, possibly attributable to fixation conditions. These result indicate that MSI and immunohistochemical loss of expression of hMLH-1 or hMSH-2 have the same value as the marker for MTS; with 100% specificity. Presently, only two MTS families with an hMLH-1 mutation have been described in the literature, compared to many reports linking MTS to a germ-line hMSH-2 mutation (17, 18) . In our study, loss of expression of hMLH-1 and hMSH-2 mutation was encountered in equal frequency, making a preferential association of MTS with a hMSH-2 germ-line mutation less likely. However, no family history is available, and not all patients may be independent. Therefore, our findings concerning the occurrence of hMLH-1 or hMSH-2 mutations in MTS cannot be generalized.
In this investigation, MSI was only seen in those with a history of both SGC and intestinal carcinomas. But patients with apparently sporadic SGC could have MTS. Previous studies show that 41% of the MTS patients have SGC as the initial malignancy; alone or concomitant with an internal neoplasm. Our study indicates that MSI or loss of expression of hMLH-1 or hMSH-2 in SGC predicts the presence of MTS. It is likely that the MSI status of other MTS-related skin tumors (such as sebaceous adenomas and sebaceous epitheliomas) might also predict the presence of MTS. Identification of MTS has important practical consequences (e.g., genetic follow-up and counseling) for the patient and family. Close follow-up of MTS patients is needed in both the MSI-positive and MSI-negative subgroups. Patients with an MSI-positive tumor or immunohistochemical loss of expression of one of the MMR genes should be offered MMR gene germ-line mutation analysis in a specialized center. Further studies are needed to identify the molecular mechanism leading to the MSI-negative variant of MTS.
| FOOTNOTES |
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1 Supported by the Netherlands Digestive Disease
Foundation (Grant WS 97-75). ![]()
2 To whom requests for reprints should be
addressed, at Academic Medical Center, Department of Pathology,
Meibergdreef 9, 1105 AZ Amsterdam, the Netherlands. Phone:
31-20-5665635; Fax: 31-20-6960389; E-mail: g.j.offerhaus{at}amc.uva.nl ![]()
3 The abbreviations used are: MTS, Muir-Torre
syndrome; SGC, sebaceous gland carcinoma; MMR, mismatch repair; HNPCC,
hereditary nonpolyposis colorectal cancer; MSI, microsatellite
instability; CRC, colorectal carcinoma; KA,
keratoacanthoma; IHC, immunohistochemistry. ![]()
Received 11/15/99; revised 2/ 4/00; accepted 2/ 7/00.
| REFERENCES |
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