Different genetic pathways in the development of periocular sebaceous gland carcinomas in presumptive Muir-Torre syndrome patients

Incidence and molecular characteristics of deficient mismatch repair conditions across nine different tumors and identification of germline variants involved in Lynch-like syndrome

BACKGROUND

Based on molecular characteristics, deficient DNA mismatch repair (dMMR) solid tumors are largely divided into three categories: somatically MLH1-hypermethylated tumors, Lynch syndrome (LS)-associated tumors, and Lynch-like syndrome (LLS)-associated tumors. The incidence of each of these conditions and the corresponding pathogenic genes related to LLS remain elusive.

METHODS

We identified dMMR tumors in 3609 tumors from 9 different solid organs, including colorectal cancer, gastric cancer, small-bowel cancer, endometrial cancer, ovarian cancer, upper urinary tract cancer, urinary bladder cancer, prostate cancer, and sebaceous tumor, and comprehensively summarized the characterization of dMMR tumors. Characterization of dMMR tumors were performed as loss of at least one of MMR proteins (MLH1, MSH2, MSH6, and PMS2), by immunohistochemistry, followed by MLH1 promotor methylation analysis and genetic testing for MMR genes where appropriate. Somatic variant analysis of MMR genes and whole exome sequencing (WES) were performed in patients with LLS.

RESULTS

In total, the incidence of dMMR tumors was 5.9% (24/3609). The incidence of dMMR tumors and the proportion of the three categorized dMMR tumors varied considerably with different tumor types. One to three likely pathogenic/pathogenic somatic MMR gene variants were detected in 15 out of the 16 available LLS tumors. One patient each from 12 patients who gave consent to WES demonstrated non-MMR germline variants affect function (POLQ or BRCA1).

CONCLUSIONS

Our data regarding the LS to LLS ratio would be useful for genetic counseling in patients who are suspected to have LS, though the genetic backgrounds for the pathogenesis of LLS need further investigation.

[Epigenetic changes in the promoter of the fragile histidine triad (FHIT) gene in human sebocytes under the influence of in vitro culture]

BACKGROUND

Due to the lack of tumor suppressor function of the fragile histidine triad (FHIT) gene product, sebaceous gland carcinomas can develop.

OBJECTIVE

The model of the sebocyte cell line SZ95 was used to identify methylated CpG islands at the 5'-end of the FHIT gene and the decrease of gene expression as well as the increase of double-stranded (ds) DNA breaks were examined.

MATERIAL AND METHODS

Methylation, immunofluorescence analysis, promotor sequencing and treatment of SZ95 cells with 5‑azacytidine/trichostatin A (TSA).

RESULTS

The cultivation was accompanied by an increasing methylation of the CpG islands, a decrease of the FHIT gene expression and an accumulation of ds-DNA breaks. Treatment with 5‑azacytidine/TSA showed a decrease in DNA methylation and a re-expression of FHIT transcripts.

DISCUSSION

Epigenetic changes in the cellular genome are caused by in vitro cell culture. Consequently, a positive selection of sebocytes with an epigenetically inactivated FHIT locus occurs.

Muir-Torre Syndrome Associated Periocular Sebaceous Neoplasms: Screening Patterns in the Literature and in Clinical Practice

Background

Muir-Torre syndrome (MTS) is defined clinically as the association of cutaneous sebaceous neoplasm and visceral malignancy. Ancillary tests are considered crucial for diagnosis. Although screening guidelines for MTS, including the Mayo MTS scoring system, have been proposed, there are no ophthalmic site-specific guidelines.

Summary

A literature review conducted by PubMed search for articles describing patients with periocular sebaceous neoplasm and MTS disclosed 31 publications describing 60 patients, 36 (60%) of whom fulfilled clinical criteria for MTS, 6 (10%) whose diagnosis was based on screening ancillary studies, 14 (23%) who fulfilled clinical criteria and had supporting screening ancillary studies, and 4 (7%) who fulfilled clinical criteria and had supporting diagnostic genetic testing. Most patients were male (34 vs. 15 females), with a median age of 59 years (range 37-79 years). The most common diagnosis was sebaceous carcinoma (40/60, 67%), followed by sebaceous adenoma (16/60, 27%), followed by other tumors with sebaceous differentiation (4/60, 6%). The periocular lesions were identified prior to visceral malignancy in 10 out of 45 (22%) cases, after visceral malignancy in 34 out of 45 (76%) cases, and concurrently with visceral malignancy in 1 out of 45 (2%) cases. Immunohistochemistry for mismatch repair proteins was performed in 41 out of 60 (68%) and 14 out of 38 (37%) of the tumors had lost MSH2. Based on Mayo-MTS scores of 2 or greater, and after removing visceral malignancies not included in their scoring algorithm, 26 out of 30 of patients (87%) with complete data were considered to be appropriate candidates for further work-up. A survey of current practice was conducted by questionnaires, distributed to ophthalmic pathologists, ocular oncologists, and oculoplastic surgeons from national and international professional societies. Of the 103 physicians who participated in the survey, 91 (88%) felt that MTS evaluation guidelines were not sufficiently clear.

Key Messages

Our findings suggest that Mayo MTS screening guidelines may be applicable to periocular sebaceous neoplasms. The uncertainty of ophthalmic specialists about optimal screening guidelines for MTS reflects the heterogeneity of defining criteria for MTS and limited molecular genetic data. Larger studies with detailed clinical, histopathologic, and molecular genetic data are required to formally assess screening guidelines for MTS in patients with periocular sebaceous neoplasms.

Mechanisms shaping the mutational landscape of the FRA3B/FHIT-deficient cancer genome

Genome instability is an enabling characteristic of cancer that facilitates the acquisition of oncogenic mutations that drive tumorigenesis. Underlying much of the instability in cancer is DNA replication stress, which causes both chromosome structural changes and single base-pair mutations. Common fragile sites are some of the earliest and most frequently altered loci in tumors. Notably, the fragile locus, FRA3B, lies within the fragile histidine triad (FHIT) gene, and consequently deletions within FHIT are common in cancer. We review the evidence in support of FHIT as a DNA caretaker and discuss the mechanism by which FHIT promotes genome stability. FHIT increases thymidine kinase 1 (TK1) translation to balance the deoxyribonucleotide triphosphates (dNTPs) for efficient DNA replication. Consequently, FHIT-loss causes replication stress, DNA breaks, aneuploidy, copy-number changes (CNCs), small insertions and deletions, and point mutations. Moreover, FHIT-loss-induced replication stress and DNA breaks cooperate with APOBEC3B overexpression to catalyze DNA hypermutation in cancer, as APOBEC family enzymes prefer single-stranded DNA (ssDNA) as substrates and ssDNA is enriched at sites of both replication stress and DNA breaks. Consistent with the frequent loss of FHIT across a broad spectrum of cancer types, FHIT-deficiency is highly associated with the ubiquitous, clock-like mutation signature 5 occurring in all cancer types thus far examined. The ongoing destabilization of the genome caused by FHIT loss underlies recurrent inactivation of tumor suppressors and activation of oncogenes. Considering that more than 50% of cancers are FHIT-deficient, we propose that FRA3B/FHIT fragility shapes the mutational landscape of cancer genomes.

Identification of Fhit as a post-transcriptional effector of Thymidine Kinase 1 expression

FHIT is a genome caretaker gene that is silenced in >50% of cancers. Loss of Fhit protein expression promotes accumulation of DNA damage, affects apoptosis and epithelial-mesenchymal transition, though molecular mechanisms underlying these alterations have not been fully elucidated. Initiation of genome instability directly follows Fhit loss and the associated reduced Thymidine Kinase 1 (TK1) protein expression. The effects on TK1 of Fhit knockdown and Fhit induction in the current study confirmed the role of Fhit in regulating TK1 expression. Changes in Fhit expression did not impact TK1 protein turnover or transcription from the TK1 promoter, nor steady-state levels of TK1 mRNA or turnover. Polysome profile analysis showed that up-regulated Fhit expression resulted in decreased TK1 RNA in non-translating messenger ribonucleoproteins and increased ribosome density on TK1 mRNA. Fhit does not bind RNA but its expression increased luciferase expression from a transgene bearing the TK1 5'-UTR. Fhit has been reported to act as a scavenger decapping enzyme, and a similar result with a mutant (H96) that binds but does not cleave nucleoside 5',5'-triphosphates suggests the impact on TK1 translation is due to its ability to modulate the intracellular level of cap-like molecules. Consistent with this, cells expressing Fhit mutants with reduced activity toward cap-like dinucleotides exhibit DNA damage resulting from TK1 deficiency, whereas cells expressing wild-type Fhit or the H96N mutant do not. The results have implications for the mechanism by which Fhit regulates TK1 mRNA, and more broadly, for its modulation of multiple functions as tumor suppressor/genome caretaker.

JAAD Grand Rounds quiz: A subcutaneous nodule on the right shoulder

LEARNING OBJECTIVES

At the conclusion of this learning activity, physician participants should be able to assess their own diagnostic and patient management skills and use the results of this exercise to help determine personal learning needs. Instructions: In answering each question, refer to the specific directions provided. Because it is often necessary to provide information occurring later in a series that give away answers to earlier questions, please answer the questions in each series in sequence.

The FHIT gene product: tumor suppressor and genome "caretaker"

The FHIT gene at FRA3B is one of the earliest and most frequently altered genes in the majority of human cancers. It was recently discovered that the FHIT gene is not the most fragile locus in epithelial cells, the cell of origin for most Fhit-negative cancers, eroding support for past claims that deletions at this locus are simply passenger events that are carried along in expanding cancer clones, due to extreme vulnerability to DNA damage rather than to loss of FHIT function. Indeed, recent reports have reconfirmed FHIT as a tumor suppressor gene with roles in apoptosis and prevention of the epithelial-mesenchymal transition. Other recent works have identified a novel role for the FHIT gene product, Fhit, as a genome "caretaker." Loss of this caretaker function leads to nucleotide imbalance, spontaneous replication stress, and DNA breaks. Because Fhit loss-induced DNA damage is "checkpoint blind," cells accumulate further DNA damage during subsequent cell cycles, accruing global genome instability that could facilitate oncogenic mutation acquisition and expedite clonal expansion. Loss of Fhit activity therefore induces a mutator phenotype. Evidence for FHIT as a mutator gene is discussed in light of these recent investigations of Fhit loss and subsequent genome instability.

Molecular pathology of skin neoplasms of the head and neck

CONTEXT

Skin neoplasms include the most common malignancies affecting humans. Many show an ultraviolet (UV)-induced pathogenesis and often affect the head and neck region.

OBJECTIVE

To review literature on cutaneous neoplasms that show a predilection for the head and neck region and that are associated with molecular alterations.

DATA SOURCES

Literature review.

CONCLUSIONS

Common nonmelanoma skin cancers, such as basal and squamous cell carcinomas, show a UV-induced pathogenesis. Basal cell carcinomas are characterized by molecular alterations of the Hedgehog pathway, affecting patched and smoothened genes. While squamous cell carcinomas show UV-induced mutations in several genes, driver mutations are only beginning to be identified. In addition, certain adnexal neoplasms also predominantly affect the head and neck region and show interesting, recently discovered molecular abnormalities, or are associated with hereditary conditions whose molecular genetic pathogenesis is well understood. Furthermore, recent advances have led to an increased understanding of the molecular pathogenesis of melanoma. Certain melanoma subtypes, such as lentigo maligna melanoma and desmoplastic melanoma, which are more often seen on the chronically sun-damaged skin of the head and neck, show differences in their molecular signature when compared to the other more common subtypes, such as superficial spreading melanoma, which are more prone to occur at sites with acute intermittent sun damage. In summary, molecular alterations in cutaneous neoplasms of the head and neck are often related to UV exposure. Their molecular footprint often reflects the histologic tumor type, and familiarity with these changes will be increasingly necessary for diagnostic and therapeutic considerations.

Hypermethylation of the CDKN2A gene promoter is a frequent epigenetic change in periocular sebaceous carcinoma and is associated with younger patient age

Periocular sebaceous carcinoma is an aggressive neoplasm with significant morbidity and mortality. Its pathogenesis is poorly understood. It is only rarely associated with Muir-Torre syndrome. Previous studies from Asian countries, have suggested that human papillomavirus (HPV) infection plays a role in the pathogenesis and overexpression of p16(INK4a), a surrogate marker of HPV infection, have also been reported. However, data from western countries seem contradictory. In order to clarify and explore the molecular and epigenetic basis of HPV, CDKN2A status and role of microsatellite instability in the development of periocular sebaceous carcinoma, 24 cases of periocular sebaceous carcinoma were analyzed for the expression of p16(INK4a) and mismatch repair proteins (MLH1, MSH2, MSH6 and PMS2) via immunohistochemistry. Nested polymerase chain reaction (PCR) and genechip HPV typing were used to detect HPV infection and decide its genotype when present. PCR amplification using a consensus primer pair was also performed to detect β-HPV. The methylation status of CDKN2A promoter region was studied by methylation-specific polymerase chain reaction. HPV-positivity was demonstrated in only one of our cases (HPV 16), while another case showed p16(INK4a) overexpression. All cases showed preserved expression of mismatch repair proteins. CDKN2A promoter hypermethylation was noted in nearly half of our cases (11/24) and was associated with younger patient age (P = .013). Our results showed that periocular sebaceous carcinoma is rarely associated with HPV and microsatellite instability. Higher frequency of CDKN2A promoter hypermethylation in younger patients implies a significant epigenetic role in tumor development in this age group.

Muir-Torre Syndrome in a Middle-Aged Chinese Patient with Sebaceous Carcinoma of the Eyelid

Muir-Torre syndrome is a rare, autosomal dominant condition characterized by the presence of a skin tumor of sebaceous differentiation and visceral malignancies. We reviewed the case of a 46-year-old Chinese man who had a bleeding mass over the right upper eyelid. He had a history of colon cancer and a family history satisfying the Amsterdam criteria for hereditary non-polyposis colorectal cancer syndrome with germline mutation in the MutS homolog-2 gene. The eyelid lesion was excised completely and submitted for histopathologic examination which showed sebaceous carcinoma. Frozen section and conjunctival map biopsy showed no residual malignancy or local metastasis. Post-operative positron-emission tomography with combined computed tomography did not reveal any residual or visceral malignancy. He had no recurrence in the 32-month follow-up period. We should consider Muir-Torre syndrome in patients with sebaceous carcinoma, especially in the presence of personal and/or family history of visceral malignancies.

Initiation of genome instability and preneoplastic processes through loss of Fhit expression

Genomic instability drives tumorigenesis, but how it is initiated in sporadic neoplasias is unknown. In early preneoplasias, alterations at chromosome fragile sites arise due to DNA replication stress. A frequent, perhaps earliest, genetic alteration in preneoplasias is deletion within the fragile FRA3B/FHIT locus, leading to loss of Fhit protein expression. Because common chromosome fragile sites are exquisitely sensitive to replication stress, it has been proposed that their clonal alterations in cancer cells are due to stress sensitivity rather than to a selective advantage imparted by loss of expression of fragile gene products. Here, we show in normal, transformed, and cancer-derived cell lines that Fhit-depletion causes replication stress-induced DNA double-strand breaks. Using DNA combing, we observed a defect in replication fork progression in Fhit-deficient cells that stemmed primarily from fork stalling and collapse. The likely mechanism for the role of Fhit in replication fork progression is through regulation of Thymidine kinase 1 expression and thymidine triphosphate pool levels; notably, restoration of nucleotide balance rescued DNA replication defects and suppressed DNA breakage in Fhit-deficient cells. Depletion of Fhit did not activate the DNA damage response nor cause cell cycle arrest, allowing continued cell proliferation and ongoing chromosomal instability. This finding was in accord with in vivo studies, as Fhit knockout mouse tissue showed no evidence of cell cycle arrest or senescence yet exhibited numerous somatic DNA copy number aberrations at replication stress-sensitive loci. Furthermore, cells established from Fhit knockout tissue showed rapid immortalization and selection of DNA deletions and amplifications, including amplification of the Mdm2 gene, suggesting that Fhit loss-induced genome instability facilitates transformation. We propose that loss of Fhit expression in precancerous lesions is the first step in the initiation of genomic instability, linking alterations at common fragile sites to the origin of genome instability.

Normal cells have robust mechanisms to maintain the proper sequence of their DNA; in cancer cells these mechanisms are compromised, resulting in complex changes in the DNA of tumors. How this genome instability begins has not been defined, except in cases of familial cancers, which often have mutations in genes called “caretaker” genes, necessary to preserve DNA stability. We have defined a mechanism for genome instability in non-familial tumors that occur sporadically in the population. Certain fragile regions of our DNA are more difficult to duplicate during cell division and are prone to breakage. A fragile region, FRA3B, lies within the FHIT gene, and deletions within FRA3B are common in precancer cells, causing loss of Fhit protein expression. We find that loss of Fhit protein causes defective DNA replication, leading to further DNA breaks. Cells that continue DNA replication in the absence of Fhit develop numerous chromosomal aberrations. Importantly, cells established from tissues of mice that are missing Fhit undergo selection for increasing DNA alterations that can promote immortality, a cancer cell hallmark. Thus, loss of Fhit expression in precancer cells is the first step in the initiation of genomic instability and facilitates cancer development.

p53 staining correlates with tumor type and location in sebaceous neoplasms

Sebaceous neoplasms are commonly considered in their relationship to the Muir-Torre syndrome and the now well-documented loss of DNA mismatch repair proteins leading to microsatellite instability. However, sebaceous neoplasms showing microsatellite instability comprise only a subset of this group of tumors, and thus, alternative tumorigenic mechanisms must exist. This article explores the relationship of p53, a tumor suppressor implicated in other cutaneous malignancies, and sebaceous neoplasia. We examined 94 sebaceous tumors from 92 patients. Tumors with strong nuclear p53 staining were significantly associated with the diagnosis of sebaceous carcinoma compared with benign sebaceous lesions, most notably for periocular carcinomas. Importantly, nuclear mismatch repair protein expression was intact in all lesions showing p53 alterations, suggesting that p53 dysfunction may represent a divergent pathway in the molecular pathogenesis of these tumors.

Sebaceous neoplasia and the Muir-Torre syndrome: important connections with clinical implications

Sebaceous neoplasia comprises a spectrum ranging from benign to malignant. Proper histological identification is important for treatment, prognosis and potential association with the Muir-Torre syndrome (MTS). Our increased understanding of the significance and pathogenesis of these tumours has led to improved risk stratification, screening recommendations, and treatment of patients with an initial presentation of a sebaceous tumour. This review focuses on the diagnostic and histological features of sebaceous lesions, the MTS, and recent insights into the molecular pathogenesis of sebaceous tumours.

Differential MSH2 promoter methylation in blood cells of Neurofibromatosis type 1 (NF1) patients

Neurofibromatosis type 1 (NF1) is caused by NF1 gene mutations. The phenotype is highly variable, with 'modifiers' being discussed as potential determinants. Mismatch repair deficiency was shown to cause NF1 mutations, but constitutional mutation of mismatch repair genes was identified only once in a NF1 patient. We aimed to analyze whether DNA methylation of mismatch repair gene promoters, known to lead to transcriptional silencing, is associated with increased tumor load in NF1 defined by the number of cutaneous neurofibromas. Leukocyte DNA of 79 controls and 79 NF1 patients was investigated for methylation of mismatch repair genes MLH1, MSH2, MSH6, and PMS2 by methylation-specific PCR and pyrosequencing. MLH1, MSH6, and PMS2 promoters were not methylated. By contrast, we found promoter methylation of MSH2 with a higher rate of methylation in NF1 patients compared with controls. Furthermore, when comparing NF1 patients with a low vs those with a high number of cutaneous neurofibromas, MSH2 promoter methylation was significantly different. In patients with a high tumor burden, methylation of two (out of six) CpGs was enhanced. This finding was not confounded by age. In conclusion, enhanced methylation involving transcription start points of mismatch repair genes, such as MSH2 in NF1, has not been described so far. Methylation-induced variability of MSH2 gene expression may lead to variable mismatch repair capacity. Our results may point toward a role of MSH2 as a modifier for NF1, although the amount of DNA methylation and subsequent gene expression in other cell types of NF1 patients needs to be elucidated.

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.

Loss of Rad51c leads to embryonic lethality and modulation of Trp53-dependent tumorigenesis in mice

RecA/Rad51 protein family members (Rad51, Rad51b, Rad51c, Rad51d, Xrcc2, and Xrcc3) are essential for DNA repair by homologous recombination, and their role in cancers has been anticipated. Here we provide the first direct evidence for a tumor suppressor function for a member of the Rad51 family. We show that Rad51c deficiency leads to early embryonic lethality, which can be delayed on a Trp53-null background. To uncover the role of Rad51c in tumorigenesis, we have exploited the fact that Rad51c and Trp53 are both closely located on the mouse chromosome 11. We have generated double heterozygous (DH) mice carrying mutant alleles of both genes either on different (DH-trans) or on the same chromosome (DH-cis), the latter allowing for a deletion of wild-type alleles of both genes by loss of heterozygosity. DH-trans mice, in contrast to DH-cis, developed tumors with latency and spectrum similar to Trp53 heterozygous mice. Strikingly, Rad51c mutation in DH-cis mice promoted the development of tumors of specialized sebaceous glands and suppressed tumors characteristic of Trp53 mutation. In addition, DH-cis females developed tumors significantly earlier than any other group.

Deletions of BRCA1/2 and p53 R248W gain-of-function mutation suggest impaired homologous recombination repair in fragile histidine triad-negative sebaceous gland carcinomas

BACKGROUND

Sebaceous gland carcinomas represent rare malignancies of the skin and some 60% of them demonstrate high-grade microsatellite instability on the background of a defective mismatch repair system. However, a significant fraction of periocular sebaceous gland carcinomas exhibits microsatellite stability associated with a frequent loss of the candidate tumour suppressor fragile histidine triad (FHIT).

OBJECTIVES

We hypothesized that in those sebaceous gland carcinomas with microsatellite stability and loss of FHIT, effector molecules participating in homologous recombination repair (HRR), such as BRCA1/2, could be somatically inactivated.

METHODS

A pilot series of 10 paraffin-embedded sebaceous gland carcinoma specimens with a defined FHIT status was studied for loss of heterozygosity (LOH) events in the genes BRCA1, BRCA2, FHIT and WWOX. We sequenced the coding exons 5-8 of the p53 gene.

RESULTS

Sebaceous gland carcinomas with FHIT negativity displayed LOH and biallelic deletions of the BRCA1 gene in five of 10 (50%) of the sebaceous gland carcinoma specimens analysed. Tumour-specific genomic losses close to BRCA2 were also uncovered. A homozygous p53 R248W gain-of-function mutation as the result of a CGG to TGG transition was identified in one of seven sebaceous gland carcinomas. It has been demonstrated previously that p53 R248W mutants inactivate ATM-directed HRR. This particular sebaceous gland carcinoma presented with concomitant genomic deletions at the BRCA1 and BRCA2 loci, and also at the constitutively fragile sites FRA3B/FHIT and FRA16D/WWOX.

CONCLUSIONS

Our study demonstrates for the first time that microsatellite-stable FHIT-negative sebaceous gland carcinomas accumulate mutations that target central components of the HRR network. This observation will prompt investigations in synthetic lethality of BRCA-deficient sebaceous gland carcinomas by therapeutic poly(ADP-ribose) polymerase inhibitors.

Differenzialdiagnose und Therapieoptionen bei Tumoren der Konjunktiva

The diagnostic classification of most conjunctival tumors is based on case history, inspection, and examination with the slit lamp microscope. Further imaging procedures are rarely indicated when malignant processes are not circumscribed. Clinical classification then also includes palpation and echographic examination of regional lymph nodes. Pigmented and nonpigmented melanocytic nevi are the most frequent conjunctival tumors. An important practical biomicroscopic cardinal symptom of the most frequent nevi is the presence of epithelial pseudocysts. Essential in practice is the histopathological confirmation of the clinical diagnosis, e.g., distinguishing between nonpigmented melanomas and sebaceous gland carcinomas with a pagetoid growth pattern or squamous cell carcinomas. Depending on the course and findings, the following therapeutic measures can be indicated: cryotherapy, chemotherapy, radiotherapy, modified enucleation, orbital exenteration, or a combination of different methods.

Telomerase expression in sebaceous lesions of the skin

BACKGROUND

Recent studies have demonstrated telomerase expression in ophthalmologic sebaceous carcinoma and have suggested possible diagnostic utility in distinguishing these neoplasms from sebaceous adenomas. The aim of this study was to evaluate telomerase expression via human telomerase reverse transcriptase (hTERT) immunohistochemical staining in a spectrum of sebaceous lesions of the skin.

METHODS

Paraffin-embedded sections from sebaceous hyperplasia (11), nevus sebaceus (22), sebaceous adenoma (19), sebaceoma (11), and sebaceous carcinoma (14) were evaluated for intensity (0 to 3+) and pattern of anti-hTERT staining.

RESULTS

Strong (2 to 3+) hTERT staining was observed in nucleoli of germinative cells and immature sebocytes in all sebaceous lesions, whereas mature sebocytes were negative. The distribution pattern paralleled features seen by routine haematoxylin and eosin-stained sections.

CONCLUSIONS

All hyperplastic and neoplastic sebaceous skin lesions expressed hTERT in this immunohistochemical study. The pattern of staining was predictive of the histologic pattern of the process but does not significantly add to our diagnostic armamentarium of sebaceous lesions.