Microsatellite instability in benign skin lesions in hereditary non-polyposis colorectal cancer syndrome

Immuno-Interception for Patients with High-Risk Cancer

Cancer immune-interception for prevention of recurrence in patients with high-risk familial cancer like Muir-Torre syndrome or Lynch syndrome using immune checkpoint blockade inhibitors is a promising approach. Albeit, as described in a case report by Pollak and colleagues in the April 2020 issue of Cancer Prevention Research, it has the potential to be used as immune-interceptive with alternative dosing regimens for cancers with microsatellite instability. The combination of additional cancer preventive and immunopreventive approaches, such as vaccines and minimal dose of immune checkpoint blockade inhibitors, is another unexplored modality for cancer interception in high-risk individuals.

Antitumor imidazo[5,1-d]-1,2,3,5-tetrazines: compounds modified at the 3-position overcome resistance in human glioblastoma cell lines

Imidazotetrazines substituted at the N-3 position overcome resistance or tolerance to temozolomide conferred, respectively, by MGMT or DNA MMR defects.

Family with MSH2 mutation presenting with keratoacanthoma and precancerous skin lesions

Muir-Torre syndrome (MTS) is a familial cancer syndrome characterized by a predisposition to keratoacanthoma (KA) and sebaceous tumors. Although MTS and hereditary non-polyposis colorectal cancer (HNPCC) share the same genetic alterations in mismatch repair (MMR) genes, the other skin lesions in MTS or HNPCC have been only rarely reported. We report a family with an MSH2 mutation c.1126_1127delTT (p.Leu376Thrfs*12). A 46-year-old male proband developed KA with sebaceous differentiation, colon cancer and gastric cancer, and fulfilled the diagnostic criteria for MTS. His 80-year-old mother, diagnosed with HNPCC, presented with multiple gastrointestinal tract cancers, Bowen's disease and actinic keratosis. Immunostaining revealed attenuated MSH2 protein expression in KA, as well as in Bowen's disease and actinic keratosis lesions. These findings suggest that MMR gene abnormality is also critical in the development of benign or malignant cutaneous tumors such as actinic keratosis and Bowen's disease in MTS/HNPCC patients.

Muir-Torre syndrome: Facts and controversies

The cutaneous presentation of a tumor sometimes has implications for a patient and his or her family, and Muir-Torre syndrome is an example of this. Because a single skin lesion can have broad consequences, it is important for clinicians to be aware of Muir-Torre syndrome. The definition, potential clues, the role of ancillary testing (microsatellite, immunohistochemical, and genetic), and screening recommendations are reviewed.

Towards identification of hereditary DNA mismatch repair deficiency: sebaceous neoplasm warrants routine immunohistochemical screening regardless of patient's age or other clinical characteristics

Although the significance of immunohistochemical detection of DNA mismatch repair proteins and/or microsatellite instability testing in identifying patients at risk for germline deficiency in DNA mismatch repair genes is well established in colorectal carcinomas, the proper use of such techniques in sebaceous neoplasms, another tumor type that has been implicated in patients with hereditary DNA mismatch repair deficiency, has not been clearly defined. In this study, we stratified a series of 27 patients with 1 or more sebaceous neoplasms based on the pattern of immunohistochemical expression of MLH1, MSH2, MSH6, and PMS2, and comparatively analyzed their clinical and pathologic characteristics, including tumor-infiltrating lymphocytes and peritumoral lymphocytic response as determined by immunohistochemical staining for CD3. The study tissue samples included 30 sebaceous carcinomas, 14 sebaceous adenomas, and 7 sebaceous hyperplasias, along with 8 concurrent nonsebaceous lesions from 6 patients. Overall, 12 of the 27 (44%) patients showed abnormal IHC staining with mismatch repair proteins in their sebaceous tumors, the most commonly seen abnormality being concurrent loss of MSH2 and MSH6 (8/12, 67%). Sebaceous adenomas and carcinomas occurring in the same patients showed an identical staining pattern, as did hereditary nonpolyposis colorectal cancer-related nonsebaceous tumors in the same patients. When compared with cases that had normal expression of the mismatch repair proteins, cases with abnormal expression tended to be younger (median age, 56.5 y vs. 68 y), more likely to involve sites outside the head and neck (9/12 vs. 0/15), and more likely to have synchronous or metachronous visceral malignancies (8/12 vs. 3/15) and a positive family history. Furthermore, sebaceous tumors with abnormal expression had significantly higher CD3-positive tumor-infiltrating lymphocytes and peritumoral lymphocytic response. Thus, all these factors (age less than 60 y, involvement of nonhead and neck sites, visceral malignancy, family history fulfilling at least Bethesda guidelines, and lymphocytic infiltration) bore informative value in predicting abnormal expression of DNA mismatch repair proteins. However, their sensitivity was only modest, being 58%, 75%, 67%, 78%, and 75%, respectively. On such a premise, given that sebaceous neoplasms are only infrequently encountered, and that immunohistochemistry is easily available and reasonably reliable, we recommend that, when there exists a desire to identify hereditary DNA mismatch repair deficiency, routine immunohistochemical detection of DNA mismatch repair proteins be performed in all sebaceous neoplasms regardless of patient's age or other clinical characteristics.

Muir-Torre syndrome

Muir-Torre syndrome is an autosomal-dominant skin condition of genetic origin, characterised by tumours of the sebaceous gland or keratoacanthoma that are associated with visceral malignant diseases. The cutaneous characteristics of Muir-Torre syndrome are sebaceous adenoma, epithelioma, carcinoma, or multiple keratoacanthomas, whereas visceral malignant diseases include colorectal, endometrial, urological, and upper gastrointestinal tumours. Although Muir-Torre syndrome has a striking familial association and features of autosomal-dominant transmission, it can arise in individuals without a family history or any known mutations. Clinical and biomolecular evidence has suggested that there are two types of Muir-Torre syndrome. The most common is a variant of hereditary non-polyposis colorectal cancer, which is characterised by defects in mismatch repair genes and early-onset tumours. The second type does not show deficiency in mismatch repair and its pathogenesis remains undefined. Diagnosis of these rare sebaceous lesions warrants the search for associated internal malignant diseases: the peculiarity of skin lesions and their biomolecular characterisation with microsatellite instability analysis and immunohistochemistry could be used to identify familial Muir-Torre syndrome, allowing clinicians to tailor a personalised programme to screen for skin and visceral malignant diseases in high-risk individuals.

Characterization of hMLH1 and hMSH2 gene dosage alterations in Lynch syndrome patients

BACKGROUND & AIMS

A significant proportion of Lynch syndrome cases are believed to be due to large genomic alterations in the mismatch repair genes hMLH1 and hMSH2. However, previous studies have not adequately identified the frequency and scope of such mutations, and routine clinical Lynch syndrome testing often does not include analysis for these mutations. Our aim was to characterize hMLH1 and hMSH2 genomic rearrangements in a large population of suspected Lynch syndrome patients.

METHODS

A total of 365 samples from probands referred for genetic testing for Lynch syndrome were analyzed for the presence of large genomic alterations in hMLH1 or hMSH2 by using a combination of techniques. Samples with a deletion in exons 1-6 in hMSH2 were further characterized by polymerase chain reaction to establish the presence of the hMSH2 American founder deletion.

RESULTS

An hMLH1 or hMSH2 mutation was identified in 153 cases, and, of these, 12 of 67 (17.9%) and 39 of 86 (45.3%) had a large genomic alteration in hMLH1 and hMSH2, respectively. Overall, 6 different hMLH1 and 12 different hMSH2 deletions/duplications, including 10 novel mutations, were identified. Analysis of the hMSH2 exon 1-6 deletion samples showed that 13 of 18 (72.2%) had the American founder deletion.

CONCLUSIONS

These data show a high frequency and diverse spectrum of large genomic alterations in hMLH1 and hMSH2 in suspected Lynch syndrome patients. Thus, a comprehensive mutation identification strategy that includes the ability to detect large genomic rearrangements is imperative for the clinical genetic identification of Lynch syndrome patients and families.

Different phenotypes in Muir-Torre syndrome: clinical and biomolecular characterization in two Italian families

The Muir-Torre syndrome (MTS) is an autosomal dominant genodermatosis characterized by the presence of sebaceous gland tumours, with or without keratoacanthomas, associated with visceral malignancies. We describe and characterize two families in which the ample phenotypic variability of MTS was evident. After clinical evaluation, the skin and visceral tumours of one member of a family with 'classic' MTS and one member of a family with a 'peculiar' MTS phenotype without sebaceous lesions, but with only multiple keratoacanthomas, were analysed for microsatellite instability (MSI) and by immunohistochemistry. Tumours of both individuals showed MSI, with a concomitant lack of MSH2 immunostaining in all evaluated skin and visceral lesions; moreover, in the proband of family 2 a constitutional mutation (C-->T substitution leading to a stop codon) in the MSH2 gene was identified. We conclude that the diagnosis of MTS, which is mainly clinical, should take into account an ample phenotypic variability, which includes both cases with typical cancer aggregation in families and cases characterized by the association of visceral malignancies with multiple keratoacanthomas (without sebaceous lesions), without an apparent family history of cancer.

Identification of Muir-Torre syndrome among patients with sebaceous tumors and keratoacanthomas

BACKGROUND

The Muir-Torre syndrome (MTS) is an autosomal-dominant genodermatosis characterized by the presence of sebaceous gland tumors, with or without keratoacanthomas, associated with visceral malignancies. A subset of patients with MTS is considered a variant of the hereditary nonpolyposis colorectal carcinoma, which is caused by mutations in mismatch-repair genes. The objective of the current study was to evaluate whether a combined clinical, immunohistochemical, and biomolecular approach could be useful for the identification of Muir-Torre syndrome among patients with a diagnosis of sebaceous tumors and keratoacanthomas.

METHODS

The authors collected sebaceous skin lesions and keratoacanthomas recorded in the files of the Pathology Department of the University of Modena during the period 1986-2000. Through interviews and examination of clinical charts, family trees were drawn for 120 patients who were affected by these skin lesions.

RESULTS

Seven patients also were affected by gastrointestinal tumors, thus meeting the clinical criteria for the diagnosis of MTS. In the MTS families, a wide phenotypic variability was evident, both in the spectrum of visceral tumors and in the type of skin lesions. Microsatellite instability was found in five MTS patients: These patients showed concordance with immunohistochemical analysis; moreover, a constitutional mutation in the MSH2 gene was found in 1 patient. Lack of expression of MSH2/MSH6 or MLH1 proteins was evident in the skin lesions and in the associated internal malignancies of 3 patients and 2 patients with MTS, respectively.

CONCLUSIONS

The clinical, biomolecular, and immunohistochemical characterization of sebaceous skin lesions and keratoacanthomas may be used as screening for the identification of families at risk of MTS, a disease that is difficult to recognize and diagnose.

Multiple epithelial and nonepithelial tumors in hereditary nonpolyposis colorectal cancer: characterization of germline and somatic mutations of the MSH2 gene and heterogeneity of replication error phenotypes

Hereditary nonpolyposis colorectal cancer (HNPCC) is an autosomal inherited cancer syndrome characterized by germline plus somatic mutations of DNA mismatch repair genes and familial clustering of cancers of colorectum and other visceral organs. So far, to our knowledge, there has been no proof of nonepithelial tumors in association with HNPCC. Here we report on a MSH2 frameshift HNPCC family with a carrier found to have multiple primary tumors, including endometrial hyperplasia, ovarian adenocarcinoma, skin cavernous hemangioma, and skin dermatofibrosarcoma protuberans (DFSP). We studied the replication error (RER) phenotype in noncoding (Bat-26, Bat-25, D2S123, D5S346, and D17S250) and coding (MSH3, MSH6, BAX, and TGFBR2 genes) DNA sequences, and characterized the germline and somatic mutations of the MSH2 gene in the tumors described above and in endometrial carcinomas from two of her affected siblings. RER was observed in an order of hyperplasic endometrium (6/10 markers), ovarian carcinoma (5/10 markers), endometrial carcinomas (4/9 and 3/10), DFSP (2/9 markers), and cavernous hemangioma (2/10 markers). All the tumors showed the same germline mutation of G5-->G6 frameshift at 183-187 and polymorphism of C1168T in a heterozygous pattern. In an endometrial carcinoma, deletion of the second allele of MSH2 was evident. Heterogeneous RER patterns were noted in multiple primary tumors of the same individual and in premalignant and malignant endometrial tumors from different individuals. The study demonstrated the two hits of the hMSH(2) gene as well as intra- and interindividual variations of RER phenotypes in HNPCC. The first characterized nonepithelial tumors in HNPCC seem to carry a limited panel of RER, including a framesift at the (A)(10) tract of TGFBR2.

DNA mismatch repair and the significance of a sebaceous skin tumor for visceral cancer prevention

DNA mismatch repair is a postreplicative DNA repair cascade ensuring genomic integrity. Inactivating germline mutations in DNA mismatch repair genes are responsible for hereditary non-polyposis colorectal carcinoma syndrome (HNPCC), which predisposes to various types of visceral cancer. Most associated tumors exhibit high-grade microsatellite instability. Some patients develop skin tumors of the sebaceous glands. This combined occurrence is known as Muir-Torre syndrome, which has a high probability of an underlying DNA mismatch repair defect. This is also true for individuals selected solely on the basis of sebaceous neoplasias, tumors with the highest frequency of high-grade microsatellite instability. This article focuses on the recent advances in molecular diagnostics for the detection of DNA mismatch repair defects in patients with sebaceous neoplasias, and the potential significance for the secondary prevention of visceral cancer in these patients.

Frequency of microsatellite instability in unselected sebaceous gland neoplasias and hyperplasias

Sebaceous gland neoplasias are the cutaneous manifestation of the Muir-Torre syndrome, which is known to be a phenotypical variant of hereditary nonpolyposis colorectal cancer. Both hereditary nonpolyposis colorectal cancer and Muir-Torre syndrome are caused by inherited DNA mismatch repair defects. As a prominent molecular genetic feature, all tumors associated with a DNA mismatch repair defect exhibit high microsatellite instability. So far, the frequency of DNA mismatch repair defects in patients selected solely on the basis of a sebaceous gland tumor has never been determined. In order to estimate this frequency, we assessed microsatellite instability with up to 10 microsatellite markers in a newly collected unselected series of 25 sebaceous gland neoplasias (six sebaceous adenomas, 16 sebaceous epitheliomas, three sebaceous carcinomas) in comparison to 32 sebaceous gland hyperplasias from unrelated patients. As many as 15 of the 25 sebaceous gland neoplasias (60%), but only one of the 32 sebaceous gland hyperplasias (3%), exhibited high microsatellite instability. Thus, in our study, the majority of patients with a sebaceous gland neoplasia in contrast to patients with a sebaceous gland hyperplasia are highly suspicious for an inherited DNA mismatch repair defect. On the basis of the subsequently collected tumor histories, nine of the 15 patients with a high microsatellite unstable sebaceous gland neoplasia were identified to have Muir-Torre syndrome. In none of these cases, however, were the clinical Amsterdam criteria for diagnosing hereditary nonpolyposis colorectal cancer fulfilled. In the sebaceous tumors of the remaining six patients, high microsatellite instability was an incidental finding. In two of these six patients, single relatives were known to be affected with internal cancer; however, their family histories were not suggestive of Muir-Torre syndrome or hereditary nonpolyposis colorectal cancer. In comparison with microsatellite instability screening studies in a variety of other randomly selected tumors, our study identifies sebaceous gland neoplasias as tumors with the highest frequency of high microsatellite instability reported so far, whereas sebaceous gland hyperplasia rarely exhibits high microsatellite instability. Therefore, screening for microsatellite instability in sebaceous gland neoplasias will be of great value in the detection of an inherited DNA mismatch repair defect, which predisposes to various types of internal cancers.

Microsatellite instability and immunostaining for MSH-2 and MLH-1 in cutaneous and internal tumors from patients with the Muir-Torre syndrome

BACKGROUND

Muir-Torre syndrome (MTS) is characterized by the co-existence of sebaceous gland tumors of the skin and internal malignancies. Currently, MTS is regarded as a variant of the hereditary non-polyposis colon cancer syndrome (HNPCC). Both MTS and HNPCC are secondary to germline mutations in DNA mismatch repair genes (mainly MSH-2 and MLH-1).

METHODS

Cutaneous (eight sebaceous adenomas, one sebaceous carcinoma and one keratoacanthoma) and internal tumors (four colonic adenocarcinomas, two endometrial carcinomas, two transitional cell carcinomas of renal pelvis and ureter, one adenocarcinoma of the small bowel, one ovarian carcinoma and one colonic tubular adenoma) were obtained from six patients with MTS and were subjected to microsatellite instability (MI) analysis, and to immunostaining for MLH-1 and MSH-2. MI was assessed by evaluating three (CA)n dinucleotide repeats (D2S123, D5S346, D17S250) and the mononucleotide tracts BAT 26 and BAT 25.

RESULTS

All cutaneous and internal tumors exhibited MI. An immunohistochemical concordance between all tumors within each single patient was obtained in five cases. In these five patients all tumors exhibited a lack of MSH-2 staining, consistent with a germline abnormality in this gene. In the one remaining case, the immunohistochemical staining in the sebaceous adenoma was negative for MLH-1 and positive for MSH-2, consistent with a germline alteration in MLH-1. However, the colonic adenocarcinoma in that patient showed positivity for MSH-2 and an equivocal positivity for MLH-1.

CONCLUSIONS

The results confirm that tumors from patients with MTS exhibit MI. Moreover, immunostaining for MLH-1 and MSH-2 may be useful to identify the most probable gene responsible for the disease in each family.

Loss of fragile histidine triad (FHIT) expression and microsatellite instability in periocular sebaceous gland carcinoma in patients with Muir-Torre syndrome

PURPOSE

To report fragile histidine triad expression and microsatellite instability in periocular sebaceous gland carcinoma.

DESIGN

Interventional case series.

METHODS

Biopsy specimens of periocular sebaceous gland carcinoma obtained from six patients (mean age, 60 +/- 17 years; range, 38 to 83 years, 5 male, 1 female) with Muir-Torre syndrome and histopathologically proven sebaceous gland carcinoma were studied immunohistochemically for the presence of fragile histidine triad protein. Polymerase chain reaction-based analysis of the markers BAT25, BAT26, D2S123, D5S346, and D17S250 was performed for microsatellite instability in tumorous and matching normal tissues.

RESULTS

Fragile histidine triad protein was detectable in the sebaceous gland carcinoma from one patient with microsatellite instability. It was not detectable in sebaceous gland carcinoma specimens from five patients without any evidence of microsatellite instability.

CONCLUSION

Inactivation of fragile histidine triad tumor suppressor gene or inactivation of the mismatch-repair system resulting in microsatellite instability may contribute to the development of periocular sebaceous gland carcinoma in Muir-Torre syndrome.

Microsatellite instability and its relevance to cutaneous tumorigenesis

Increasing evidence suggests that human tumors sequentially accumulate multiple mutations that cannot be explained by the low rates of spontaneous mutations in normal cells (2-3 mutations/cell). The mathematical models estimate that for the solid tumors to develop, as many as 6-12 mutations are required in each tumor cell. Therefore, to account for such high mutation rates, it is proposed that tumor cells are genetically unstable, i.e. they have genome-wide mutations at short repetitive DNA sequences called microsatellites. Microsatellite repeats are scattered throughout the human genome, primarily in the non-coding regions, and can give rise to variants with increased or reduced lengths, i.e. microsatellite instability (MSI). This instability has been reported in an increasing number of cutaneous tumors including: melanocytic tumors, basal cell carcinomas and primary cutaneous T-cell lymphomas. Moreover, MSI has been observed in skin tumors arising in the context of some hereditary disorders such as Muir-Torre syndrome, Von Recklinghausen's disease and disseminated superficial porokeratosis. While MSI in some of these disorders reflects underlying DNA replication errors, the mechanism of instability in others is still unknown. Thus far, MSI is considered to be a distinct tumorigenic pathway that reveals surprising versatility. The ramifications for cutaneous neoplasms warrant further investigation.

Loss of DNA mismatch repair proteins in skin tumors from patients with Muir-Torre syndrome and MSH2 or MLH1 germline mutations: establishment of immunohistochemical analysis as a screening test

Muir-Torre syndrome (MTS) is a rare autosomal-dominant disorder characterized by the predisposition to both sebaceous skin tumors (or multiple keratoacanthomas) and internal malignancies. A subtype of MTS is allelic to hereditary nonpolyposis colorectal cancer and is caused by germline mutations in the DNA mismatch repair genes MSH2 or MLH1. In these cases both internal and skin tumors show characteristic microsatellite instability (MSI). The aim of the present study was to determine whether immunohistochemical examination of MSH2 or MLH1 protein expression in MTS-associated skin tumors can be used as a diagnostic screening tool to identify patients with germline mutations in MSH2 or MLH1. In the present study 28 skin lesions from 17 patients (20 sebaceous gland tumors, 4 sebaceous hyperplasias, 3 keratoacanthomas, and 1 squamous cell carcinoma) were tested immunohistochemically with antibodies against MSH2 and MLH1. Eighteen of these tumors were from eight patients with known MSH2 germline mutations, two tumors were from a patient with a germline mutation in MLH1, and eight microsatellite stable sporadic skin tumors served as controls. One sample had to be excluded because of a lack of immunoreactivity. All eight microsatellite stable tumors expressed both DNA repair proteins. In 15 of the tumors from MSH2 germline mutation carriers, loss of MSH2 expression was observed, one tumor showed reduced MSH2 expression, and one tumor displayed positive immunoreactivity to MSH2. Both tumors of the MLH1 germline mutation carrier showed loss of the MLH1 protein. In conclusion, our findings demonstrate that immunohistochemical testing of MTS-related skin tumors is a reliable screening method with high predictive value for the diagnosis of the DNA mismatch repair-deficient MTS.

An association between sebaceous carcinoma and microsatellite instability in immunosuppressed organ transplant recipients

Sebaceous carcinomas are rare cutaneous appendageal tumors that may occur sporadically or in association with an internal malignancy in Muir-Torre syndrome. In Muir-Torre syndrome microsatellite instability can often be demonstrated in tumor DNA as a result of an inherited mutation in one of several known mismatch repair genes; however, the role of microsatellite instability in sporadic sebaceous carcinomas has not been previously studied. In this report we describe the clinicopathologic characteristics of a series of unselected sebaceous carcinomas and examine them for the presence of microsatellite instability. Of 10 consecutive tumors identified over a 10 y period, only one was from a patient known to have Muir-Torre syndrome. Of the nine presumed sporadic cases, five were from four renal transplant recipients and four from otherwise healthy individuals. Microsatellite instability was demonstrable in three cases: in the Muir-Torre syndrome-associated tumor and in two tumors from transplant patients. Microsatellite instability was subsequently also found in a sebaceous carcinoma from a further transplant patient prospectively sought from another institution. The presence of microsatellite instability in post-transplant sebaceous carcinomas was associated with loss of expression of the mismatch repair protein hMSH2. In summary, sebaceous gland carcinomas, while characteristic of Muir-Torre syndrome, are commonly found outside this context. Among presumed sporadic cases, our data suggest they may be over-represented in immunosuppressed renal transplant recipients. The presence of microsatellite instability in transplant-associated lesions, together with loss of hMSH2 expression suggests that immunosuppression might unmask a previously silent Muir-Torre syndrome phenotype in some cases. Alternatively, there is experimental evidence to suggest that immunosuppressive drugs, most plausibly azathioprine, could select for the emergence of a mutator phenotype and thus predispose to the development of sebaceous carcinomas. The role of mismatch repair defects in other post-transplant skin malignancies remains to be established.

Hereditary non-polyposis colorectal cancer associated with disseminated superficial porokeratosis. Microsatellite instability in skin tumours

A 73-year-old man presented with typical lesions of disseminated superficial porokeratosis (DSP) and multiple seborrhoeic keratoses on his face, trunk and extremities, and later developed a keratoacanthoma on his lip. He belonged to a cancer-prone pedigree susceptible to colonic, uterine and other internal cancers, and had a personal history of early gastric cancer and advanced adenocarcinoma of the descending colon without adenomatous polyps at age 59 years. Polymerase chain reaction amplification of skin samples for seven separate microsatellite polymorphisms revealed microsatellite instability (MSI) at multiple loci in five of six seborrhoeic keratoses and the keratoacanthoma, strongly suggesting underlying defects in DNA mismatch repair. Although no germline mutations in two mismatch repair genes hMSH2 and hMLH1 were found, our patient was recognized as having hereditary non-polyposis colorectal cancer (HNPCC) based on the family history and the findings of the microsatellite analysis of skin tumours. This confirmed the usefulness of detection of MSI in prevalent and readily accessible skin lesions, including non-sebaceous non-dysplastic tumours such as seborrhoeic keratosis in the screening of HNPCC families. Although DSP may also be inherited as an autosomal dominant condition, this particular skin disease appeared to be sporadic in our patient and, to our knowledge, no association of DSP or other forms of porokeratosis with HNPCC has previously been reported. In contrast to the seborrhoeic keratoses and keratoacanthoma, no MSI was observed in two samples from DSP lesional epidermis examined.