Keratoacanthoma and squamous cell carcinoma are distinct from a molecular perspective

Keratoacanthoma versus Squamous-Cell Carcinoma: Histopathological Features and Molecular Markers

Considerable controversy exists within the field of dermatopathology in differentiating keratoacanthoma (KA) from squamous-cell carcinoma (SCC). KAs are rapidly growing, benign squamous tumors that are typically well differentiated. This controversy stems from the diverging perspectives on the management, classification, and diagnosis of each entity. Many believe that KAs are benign neoplasms in which intervention may be unnecessary since they are self-limiting and resolve on their own. On the other hand, SCC needs to be treated, as it carries significant morbidity and mortality risks. Early diagnosis and treatment are vital to prevent serious consequences of SCC. Nevertheless, KAs may resemble SCC grossly and microscopically. Various ancillary tests, including immunohistochemical (IHC) staining, have been proposed to differentiate between these entities, though mixed patterns of expression can limit the diagnostic utility of these techniques. Research into this topic is ongoing, with newer genetic and molecular findings illuminating the previously difficult-to-understand aspects of KA and increasing our understanding of this entity. In this review, KA and SCC will be compared along the lines of histological features, genetic, immune, and molecular markers, differential diagnosis, and management to clarify the similarities, differences, and misconceptions about both entities.

Perineural Infiltration: A Comprehensive Review of Diagnostic, Prognostic, and Therapeutic Implications

ABSTRACT

Perineural infiltration refers to a neoplastic cell involvement in, around, and through the nerves. It is considered as one of the neoplastic dissemination pathways. Thus, its identification is crucial to establish the prognosis of some malignant skin neoplasms, such as squamous cell carcinoma, and explains the locally aggressive behavior of cutaneous neoplasms, such as microcystic adnexal carcinoma. We have conducted a review of malignant and benign skin tumors in which perineural infiltration has been described, and we also discuss some histopathological findings that may simulate perineural infiltration.

Distinguishing Keratoacanthoma from Well-Differentiated Cutaneous Squamous Cell Carcinoma Using Single-Cell Spatial Pathology

Keratoacanthoma (KA) is a common keratinocyte neoplasm that is regularly classified as a type of cutaneous squamous cell carcinoma (cSCC) despite demonstrating benign behavior. Differentiating KA from well-differentiated cSCC is difficult in many cases due to the substantial overlap of clinical and histological features. Currently, no reliable discriminating markers have been defined, and consequently, KAs are often treated similarly to cSCC, creating unnecessary surgical morbidity and healthcare costs. In this study, we used RNA sequencing to identify key differences in transcriptomes between KA and cSCC, which suggested divergent keratinocyte populations between each tumor. Imaging mass cytometry was then used to identify single-cell tissue characteristics, including cellular phenotype, frequency, topography, functional status, and interactions between KA and well-differentiated cSCC. We found that cSCC had significantly increased proportions of Ki67+ keratinocytes among tumor keratinocytes, which were dispersed significantly throughout non-basal keratinocyte communities. In cSCC, regulatory T-cells were more prevalent and held greater suppressive capacity. Furthermore, cSCC regulatory T-cells, tumor-associated macrophages, and fibroblasts had significant associations with Ki67+ keratinocytes as opposed to avoidances with KA, indicating a more immunosuppressive environment. Our data suggest that multicellular spatial features can serve as a foundation to enhance the histological discrimination of ambiguous KA and cSCC lesions.

Aberrant p16, p53 and Ki-67 immunohistochemistry staining patterns can distinguish solitary keratoacanthoma from cutaneous squamous cell carcinoma

Keratoacanthoma (KA) is widely considered a benign, usually self-resolving, neoplasm distinct from cutaneous squamous cell carcinoma (cSCC), while some consider KA to be indistinguishable from cSCC. Published studies indicate utility for p16, p53, Ki-67 immunostaining and elastic van Gieson (EVG) in the assessment of KA and cSCC. We compared clinical features and staining patterns for p16, p53, Ki-67 and EVG in fully excised KA, cSCC with KA-like features (cSCC-KAL) and other cSCC (cSCC-OTHER). Significant differences between KA, cSCC-KAL and cSCC-OTHER were found for head and neck location (20%, 86%, 84%), and duration <5 months (95%, 63%, 36%). KA shows both a mosaic pattern for p16 (>25-90% of neoplasm area) and peripheral graded pattern for p53 (up to 50% moderate and strong nuclear staining) in 92% compared with 0% of cSCC-KAL and 0% of cSCC-OTHER. In contrast, a highly aberrant pattern (usually null) for one or both p16 and p53, was present in 0% of KA, 83.8% of cSCC-KAL and 90.9% of cSCC-OTHER. Abnormal distribution of Ki-67 beyond the peripheral 1-3 cells was uncommon in KA (4.2%) and common in cSCC-KAL (67.6%) and cSCC-OTHER (88.4%). Moderate to striking entrapment of elastic and collagen fibres was present in the majority of KA (84%), cSCC-KAL (81%) and cSCC-OTHER (65%). KA are clinically distinct neoplasms typically of short duration occurring preferentially outside the head and neck and generally lacking aberrations of p16, p53 and Ki-67, compared with cSCC that have high rates of aberrant or highly aberrant p16, p53 and Ki-67, but EVG lacked specificity.

Radiotherapy for keratoacanthoma of facial skin: A case report and review of literature

Background

Keratoacanthoma (KA) is a benign tumor that arises from the infundibulum of hair follicles. However, some researchers believe that KA is a subtype of squamous cell carcinoma (SCC) or a borderline tumor. There are two types of KA: single-type and multiple-type. Surgical resection is the first-line treatment for KA. The treatment options for patients with large lesions who are not surgical candidates are limited. We present a case of single-type KA patients with basic diseases and large lesions that were untreatable surgically, but the lesions essentially disappeared after radiotherapy. No recurrences were discovered during the two-year follow-up.

Case Description

A 62-year-old male patient was admitted to the dermatology department of our hospital in June 2020 due to the discovery of a red papule on the right face two months prior, with occasional itching, which increased gradually. Pathological examination confirmed the diagnosis of KA. Due to the large lesions and underlying diseases, he was transferred to our radiotherapy department for radiotherapy after consultation. Since the surface of the lesion is uneven and close to the corner of the eye, we adopted intensity modulated radiation therapy (IMRT) at the beginning of radiotherapy. Following the reduction of the lesion, superficial electron beam and added a bolus with thickness of 5mm on the surface of the lesion was continued. The target dose: 42Gy/21 fractions (6MV X-ray, 22Gy; 2Gy/fraction; a total of 11 fractions, 6MeV electron beam, 20Gy; 2Gy/fraction; a total of 10 fractions). By the end of radiotherapy, the patient's facial tumor was dry and subsided. The facial tumor subsided significantly two years after radiotherapy, and the damaged skin on the face recovered to a flat shape.

Conclusions

The treatment experience of this case shows that IMRT combined with superficial electron beam radiotherapy may be an effective treatment for single-type KA patients with basic diseases and large lesions that are not suitable for surgery, and it is worth further study.

Squamous Cell Carcinoma at Split Thickness Skin Graft Donor Site: A Case Report and Review of the Literature

Squamous cell carcinoma (SCC) or keratoacanthoma (KA) development at split thickness skin graft donor sites is a documented but very rare entity. We describe a case in which a patient develops a lesion at his graft site seven weeks postoperatively. Upon pathological review, it was found to be SCC and was excised expediently thereafter. Notably, in reviewing the literature, these lesions tend to develop soon after the trauma of skin graft harvest with over half diagnosed within 3 months and a vast majority within 1 year of the operation. This is in contrast to Marjolin ulcers which take years to develop after the initial burn insult. Given the diversity of autograft indications in the reviewed literature, it seems unlikely that the burns themselves contribute to the development of SCC at the donor site. Our case highlights the need for routine surveillance of graft donor sites postoperatively with an emphasis on catching malignant sequelae.

Lower lip recurrent keratoacanthoma: A case report

BACKGROUND

This paper introduces a case of recurrent keratoacanthoma (KA). KA is a self-healing disease. Recurrence after surgical resection is rare. In this case, the local application of retinoic acid ointment after the second operation achieved a good prognosis after 2 years of follow-up.

CASE SUMMARY

A 76-year-old male patient was admitted to the hospital for "lower lip rupture and scab for 3 mo". Treatment: A rectangular incision was made in the healthy tissue about 3 mm outside the periphery of the lower lip mass, and a modified Bernard sliding flap was designed to completely remove the mass. Pathology showed (lower lip) KA. When the patient returned 6 mo after surgery, the middle mucosa of the lower lip had a bulge with a diameter of about 0.5 cm. The boundary was still clear, the surface was ulcerated. A recurrence of lower lip KA was suspected and a fan-shaped incision was performed in the healthy tissue about 5 mm outside the lesion to completely resect. Pathological showed lower lip KA had recurred. Topical application of tretinoin cream was applied once a day for 3 mo. The lower lip wounds were clean at the 2-year postoperative follow-up and the mucosa was normal.

CONCLUSION

Adjuvant retinoic acid treatment after KA surgical resection can achieve good results.

Ultrastructural Features of Keratoacanthoma—Clinical Implications

Over the years, keratoacanthomas have been described as some of the most common skin lesions with the potential for malignant transformation, thus constituting an important risk factor for the development of squamous cell carcinoma. The quantification of the risk of malignant transformation is conditioned by the clinical–morphological and etiopathogenic variability of these lesions, with a negative impact on diagnostic and therapeutic management. In this sense, the main objective of this research is to characterize from an ultrastructural perspective the specific tumour microenvironment, by using a technique with a higher resolution power than photon microscopy. Keratoacanthoma lesions from 25 patients were excised from healthy tissue and then processed by classical electron microscopy and examined with the Philips CM100 microscope. The electron microscopic study revealed structural details suggestive of malignant transformation, capturing changes at both cytoplasmic and membranous levels. The identification and description of the ultrastructural morphological substrate favouring the evolution and progression of the studied lesions correlates directly with the improvement of the prognosis and quality of life of these patients.

A clinical and biological review of keratoacanthoma

Keratoacanthoma (KA) is a common skin tumour that remains controversial regarding classification, epidemiology, diagnosis, prognosis and management. Classically, a KA manifests as a rapidly growing, well-differentiated, squamoid lesion with a predilection for sun-exposed sites in elderly people and a tendency to spontaneously regress. Historically, KAs have been considered a variant of cutaneous squamous cell carcinoma (cSCC) and are often reported as KA-type cSCC. However, the penchant for regression has led many to categorize KAs as biologically benign tumours with distinct pathophysiological mechanisms from malignant cSCC. The clinical and histopathological similarities between KA and cSCC, particularly the well-differentiated variant of cSCC, have made definitive differentiation difficult or impossible in many cases. The ambiguity between entities has led to the general recommendation for surgical excision of KAs to ensure a potentially malignant cSCC is not left untreated. This current standard creates unnecessary surgical morbidity and financial strain for patients, especially the at-risk elderly population. There have been no reports of death from a definitive KA to date, while cSCC has an approximate mortality rate of 1·5%. Reliably distinguishing cSCC from KA would shift management strategies for KAs towards less-invasive treatment modalities, prevent unnecessary surgical morbidity, and likely reduce associated healthcare costs. Herein, we review the pathophysiology and clinical characteristics of KA, and conclude on the balance of current evidence that KA is a benign lesion and distinct from cSCC.

Differences in the mitochondrial microsatellite instability of Keratoacanthoma and cutaneous squamous cell carcinoma

Keratoacanthoma (KA) is a common cutaneous neoplasm which often resembles typical squamous cell carcinoma (SCC) in both its clinical and historical presentation. Several studies have attempted to identify methods for distinguishing between KA and SCC, however, none of these have proven to play any obvious roles in these tumors. Given this we went on to evaluate mitochondrial microsatellite instability (mtMSI) in KA and SCC in an effort to understand these tumors better. DNA was isolated from paired normal and tumoral tissues donated by 57 KA patients and 43 SCC patients. MtMSI was then analyzed using eight microsatellite markers and was observed in 2 (3.5%) of the 57 KA patients and 8 (18.6%) of the 43 SCC patients, respectively. MtMSI was also shown to affect different locations depending on tumor type. In KA patients, mtMSI was detected at mitochondrial D514 D-loop and presented with (CA) n repeats, in contrast, all of the SCC patient experienced mtMSI at the D310 with (C)n repeats of the D-loop region. These differences in location were found to be significant, which may support the hypothesis that KA and SCC have different pathogenetic pathways. Our results also suggest that mtMSI may be a candidate for developing novel differential diagnostic methods for KA and SCC.

Clinical, histopathological and immunohistochemical study of keratoacanthoma

Keratoacanthoma (KA) is an epithelial tumor of the skin, classically considered as having a malignant transformation risk of 15%; however, many authors and the new World Health Organization (WHO) Classification of skin tumors consider KA as an incipient variant of the cutaneous squamous cell carcinoma (SCC). The aims of the study were to assess the clinical, histopathological (HP) and immunohistochemical (IHC) aspects of the KA and the role of these factors in malignancy occurrence. The studied group comprises 194 patients diagnosed with KA or malignant KA, hospitalized in the Clinic of Dermatology, Emergency County Hospital, Craiova, Romania, between 2006 and 2019. There were 83 males and 111 females, aged 34 to 90 years, 57.21% of the patients being from the rural environment. The histopathology diagnosed 51 KAs and 143 malignant KAs (SCCs). Clinical diagnosis had a limited value in detecting the absence or presence of malignancy in the KA lesion, due to a low accuracy (36.08% and 29.89%, respectively) and specificity (23.07% and 27.02%, respectively); therefore, the HP exam of the surgical excision specimen has a paramount importance in establishing the diagnosis. IHC analysis revealed that the immunostainings for apoptosis-associated proteins and keratinocyte proliferative activity [p53, B-cell lymphoma-2 (Bcl-2), Ki-67 and proliferating cell nuclear antigen (PCNA)] provide some arguments to differentiate between KA and SCC in the studied cases. The correlation of clinical, HP and IHC data lead to an accurate diagnosis of KA; moreover, the clinical, HP and IHC data sustain the idea that KA is a particular form of well-differentiated SCC, which require an active therapeutic attitude.

Keratoacanthoma: Update on the Debate

ABSTRACT

Keratoacanthoma (KA) is a cutaneous tumor with a biphasic pattern of growth. A rapidly growing phase is usually followed by involution. KA occurs on sun-damaged skin. There are many listed causative associations, which include some therapeutic agents. Debate continues as to whether KA is a variant of squamous carcinoma (SCC) or a separate entity. Reporting of KA versus SCC is markedly inconsistent. Reasons for inconsistency include overlapping microscopic criteria, variants of KA with more aggressive features, and possibly medicolegal concerns. Genetic studies have shown some differences between the 2 entities. Activation of apoptotic pathways has been demonstrated in KA. Genetic studies have shown a possible role of human polyomavirus 6 in the pathogenesis of at least some KAs. Given that some cases of KA have components that behave as conventional SCCs, KA can be considered as a low-grade variant of SCC with some genetic differences.

Mutational profile of skin lesions in hepatocellular carcinoma patients under tyrosine kinase inhibition: a repercussion of a wide-spectrum activity

BACKGROUND/AIM

Dermatological adverse events (DAE) in hepatocellular carcinoma (HCC) patients treated with sorafenib predicts better outcome. Some turn into skin lesions (SL) requiring pathology examination. We describe incidence, characteristics and molecular profile of SL in HCC patients treated with sorafenib.

MATERIALS AND METHODS

SL were prospectively collected in 311 HCC patients who started sorafenib. SL from sorafenib cohort were compared to those from a control patient group selected to match SL type and demographics. HRAS, KRAS and BRAF mutations were analyzed by CAST-PCR, mutated p53 and MAPK pathway activation by immunohistochemistry and immune infiltration by hematoxylin-eosin staining.

RESULTS

Eighty-eight out of 311 patients developed DAE and 7.4% SL required histological assessment. Most frequent lesions were keratoacanthomas (n = 4), squamous-cell carcinomas (SCC)(n = 5), basal-cell carcinomas (BCC)(n = 3) and seborrheic keratosis (n = 5). HRAS and KRAS mutations were detected in 4 SL, while no mutations showed in control SL. Nuclear pERK immunostaining was identified in 33.3% of cases versus 5.3% of controls. Most SL (90%) from patients with DAE were proliferative with intense immune infiltration (73%).

CONCLUSIONS

The onset of SL and their molecular profile did not impact negatively on patient's prognosis, but intense proliferation of SL may reflect compensatory activation of MAPK pathway and warrants their close monitoring.

Keratoacanthoma, committed stem cells and neoplastic aberrant infundibulogenesis integral to formulating a conceptual model for an infundibulocystic pathway to squamous cell carcinoma

Keratoacanthomas (KAs) are distinctive tumors that are defined by their clinical and histopathological features. Their relationship and distinction from squamous cell carcinoma (SCC), however, remain controversial. All cytogenic and immunohistochemical markers that have been applied in this quest have failed. A close relationship of KAs to hair follicles has been recognized. The descriptive term infundibulocystic or infundibular SCC was introduced to define a more broad-based pathway encompassing KAs. The follicular infundibulum roles in respect to neoplasia and wound healing are important elements in understanding the pathogenesis of KAs. Mouse models for KA have provided insights into the relationship of KA to follicles and SCCs. These advances and together with the diverse clinical and histopathological aspects of KA have contributed to the formulation of a conceptual pathway. The central element is that ultraviolet (UV)-mutated or activated committed infundibular stem cells are driven by the combination of a mutated oncogenic RAS pathway linked with the Wnt/beta-catenin pathway responsible for stem cell maintenance, hair follicle development, wound healing and driving KA proliferation and terminal keratinization. The existence and activation of this mutated pathway may form the basis of the paradoxical emergence of KAs and SCCs in patients receiving BRAF and PD-1 inhibitor therapy.

Myriad facades of keratocanthoma: Benignity VS malignancy

Keratoacanthoma (KA) is a self-limiting benign epithelial neoplasm. It occurs predominantly on sun-exposed areas of the body and is believed to arise from hair follicle. It shows a unique behavior in being clinically benign and microscopically malignant. Earlier it was considered as a pseudomalignant lesion but now it is believed to be pseudobenign in nature. The most common concern is related to its nosological position at the border of malignancy and benignity. We hereby report a rare case of keratoacanthomatous type of squamous cell carcinoma in an elderly female showing aggressive nature of the lesion. The various terminologies used for KA in the past have also been tabulated.

Study of Gene Expression Profiles of Breast Cancers in Indian Women

Breast cancer is the most common cancer among women globally. In India, the incidence of breast cancer has increased significantly during the last two decades with a higher proportion of the disease at a young age compared to the west. To understand the molecular processes underlying breast cancer in Indian women, we analysed gene expression profiles of 29 tumours and 9 controls using microarray. In the present study, we obtained 2413 differentially expressed genes, consisting of overexpressed genes such as COL10A1, COL11A1, MMP1, MMP13, MMP11, GJB2, and CST1 and underexpressed genes such as PLIN1, FABP4, LIPE, AQP7, LEP, ADH1A, ADH1B, and CIDEC. The deregulated pathways include cell cycle, focal adhesion and metastasis, DNA replication, PPAR signaling, and lipid metabolism. Using PAM50 classifier, we demonstrated the existence of molecular subtypes in Indian women. In addition, qPCR validation of expression of metalloproteinase genes, MMP1, MMP3, MMP11, MMP13, MMP14, ADAMTS1, and ADAMTS5 showed concordance with that of the microarray data; wherein we found a significant association of ADAMTS5 down-regulation with older age (≥55 years) of patients. Together, this study reports gene expression profiles of breast tumours from the Indian subcontinent, throwing light on the pathways and genes associated with the breast tumourigenesis in Indian women.

TPM4 promotes cell migration by modulating F-actin formation in lung cancer

Background: Tropomyosin 4 (TPM4) is a member of the tropomyosin family of actin-binding proteins. Abnormal level of TPM4 is found in several cancers, and TPM4 is considered as a potential detecting marker for ovarian cancer, breast cancer, colon cancer, keratoacanthoma and esophageal squamous cell carcinoma. In this paper, the function of TPM4 in lung cancer cell lines was determined.

Materials and methods: TPM4 knockout cells were constructed by CRISPR/CAS9 technique. TPM4 overexpression cells were also constructed based on TPM4 knockout cells. Cell growth ability was detected by MTS assay. The potency of cell motility was investigated using transwell assay and wound scratch assay. The protein levels in lung cancer cells were determined by western-blot. Immunofluorescence technique was used to image the structure of F-actin.

Results: As a result, TPM4 downregulation and TPM4 upregulation cell models were obtained successfully. Cell motility was inhibited by the suppression of TPM4 while cell migration was enhanced in TPM4 upregulated cells. But TPM4 was not involved in cell proliferation and EMT progression. Microfilaments were depolymerized result from the suppression of TPM4 expression. And F-actin assembly was increased when TPM4 was upregulated.

Conclusion: In summary, TPM4 was able to promote cell motility by altering the actin cytoskeleton directly.

Patterns of LC3A Autophagy Protein Expression in Keratoacanthomas

To investigate the expression patterns of autophagy marker light chain protein 3 (LC3A) in keratoacanthoma (KA). KAs are generally regarded as benign but malignant behavior, including rare metastases, may occur. 85 KAs were assessed for the LC3A autophagic protein by immunohistochemistry. Diffuse cytoplasmic staining and a "stone-like structure" (SLS) characterized positive expression. Thirty-four out of 85 KAs (40%) had diffuse cytoplasmic LC3A immunostaining (percentage of positive cells ranging from 5 to 60%). In contrast, only 4 of the 85 KAs (4.7%) expressed SLSs. Only one SLS was detected per histologic section of each tumor. The p53 oncoprotein was encountered in all cases with expression ranging from 1 to 90% of cells (median 30%). The Ki-67 index was expressed in 63 cases (74% of cases; range 1-50% of cells; median value 5%). Neither of these two parameters nor diffuse cytoplasmic LC3A staining was significantly correlated with SLS expression or lack thereof. Expression of SLSs, a hallmark of malignancy, was found in 4.7% of KAs. Further study is necessary to determine whether this fraction represents the exceptional cases that harbor latent malignant potential.

Cutaneous Papillomaviruses and Non-melanoma Skin Cancer: Causal Agents or Innocent Bystanders?

There is still controversy in the scientific field about whether certain types of cutaneous human papillomaviruses (HPVs) are causally involved in the development of non-melanoma skin cancer (NMSC). Deciphering the etiological role of cutaneous HPVs requires - besides tissue culture systems - appropriate preclinical models to match the obtained results with clinical data from affected patients. Clear scientific evidence about the etiology and underlying mechanisms involved in NMSC development is fundamental to provide reasonable arguments for public health institutions to classify at least certain cutaneous HPVs as group 1 carcinogens. This in turn would have implications on fundraising institutions and health care decision makers to force - similarly as for anogenital cancer - the implementation of a broad vaccination program against "high-risk" cutaneous HPVs to prevent NMSC as the most frequent cancer worldwide. Precise knowledge of the multi-step progression from normal cells to cancer is a prerequisite to understand the functional and clinical impact of cofactors that affect the individual outcome and the personalized treatment of a disease. This overview summarizes not only recent arguments that favor the acceptance of a viral etiology in NMSC development but also reflects aspects of causality in medicine, the use of empirically meaningful model systems and strategies for prevention.

MALAT1: A long non-coding RNA highly associated with human cancers

Metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), a well-known lncRNA associated with numerous diseases, particularly cancer, has received increased attention. The expression of MALAT1 was determined to be upregulated in numerous types of tumors and MALAT1 exhibited effects on tumor cell proliferation, migration, invasion and apoptosis. The abnormal expression of MALAT1 was identified in almost in every organ of the digestive system. MALAT1 performed an important role in the pathological alterations of organs that are associated with sex hormones and several reproductive system cancers. MALAT1 participates in molecular pathways. In the clinical application of MALAT1, MALAT1 was considered as a potential biomarker for the diagnosis and prediction of cancers, and may also serve as therapeutic target for treatment of specific tumors. This review summarizes the abnormal expression of MALAT1 in cancer, its significant effect on the primary features of cancer, as well as the underlying molecular mechanisms of MALAT1 in various cancers. According to studies on MALAT1, we introduce the upstream and downstream substances associated with the function of MALAT1. These reviewed studies promote the clinical application of MALAT1 in the aspect of diagnosis and treatment of different cancers, and may help point out new study directions for MALAT1.

Carcinogenicity assessment of the Hedgehog pathway inhibitor, vismodegib in Tg.rasH2 mice and Sprague-Dawley rats

Vismodegib (also known as GDC-0449) is a novel small molecule inhibitor of the Hedgehog (Hh) signaling pathway currently approved for the treatment of metastatic or locally advanced basal cell carcinoma (BCC) in humans. Its tumorigenic potential was assessed in dedicated carcinogenicity studies in rasH2 transgenic (Tg.rasH2) mice and Sprague Dawley (SD) rats. Tumorigenicity potential of vismodegib was identified in rats only and was limited to benign hair follicle tumors, including pilomatricomas and keratoacanthomas at exposures of ≥0.1-fold and ≥0.6-fold, respectively, of the steady-state exposure (AUC_0-24h) of the recommended human dose. No malignant tumors were identified in either species. Overall, the totality of pharmacology and nonclinical safety data (lack of genotoxicity, in vitro secondary pharmacological binding, and immunoregulatory effects, and limited effects on the endocrine system) suggests that the development of the benign hair follicle tumors may be related to pharmacologically-mediated disruption of hair follicle morphogenesis, although the exact mechanism of tumorigenesis is unclear. Hair follicle tumors have not been reported in vismodegib-treated patients. The relevance of this finding in rats to patients is uncertain.

Keratoacanthoma en plaque/nodule: A brief report of the clinicopathological features of five cases

Keratoacanthoma (KA) is characterized by exoendophytic growth with a central keratin-filled crater, representing the crateriform architecture. We herein report five rare cases of KA without a central keratin-filled crater. These KA cases histopathologically showed that one or a few infundibular structures/isthmic lobules had their own open keratotic pores on the surface without a common merged keratotic plug/horn, clinically representing verrucous (keratotic) plaque/nodule, namely, "KA en plaque/nodule". KA rarely but on occasion does show verrucous plaque (or nodular) lesions without a central keratin-filled crater, as the notion that KA invariably shows crateriform architecture is nonsensical.