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Some patients with basal cell carcinoma develop a large number of basal cell carcinomas during their lives. The most common underlying genetic disease that causes multiple basal cell carcinomas is basal cell naevus syndrome. Basal cell naevus syndrome is caused by a germline mutation in patched-1 (PTCH1), a tumour suppressor gene of the hedgehog signalling pathway. However, in a significant portion of patients with multiple basal cell carcinomas, no underlying genetic cause is found. Nevertheless, these patients can experience a treatment burden comparable to that of patients with basal cell naevus syndrome. They are referred to as high-frequency basal cell carcinoma patients. Hedgehog pathway inhibitors were the first group of targeted therapy for basal cell carcinomas. This study reviews the literature on hedgehog pathway inhibitor therapy for patients with basal cell naevus syndrome and high-frequency basal cell carcinoma, to provide an overview on efficacy, safety, dosing regimens, tumour resistance and reoccurrence, and health-related quality of life.

Background: Metastatic basal cell carcinoma (mBCC) is a very rare entity, and diagnosis can be challenging. Therapeutic options are limited, and response to targeted therapy is poor., Objective: To demonstrate a clonal relationship between BCCs and their metastases and to explore which hedgehog pathway-related mutations are involved in mBCC., Methods: Genetic analysis was conducted in 10 primary BCCs and their metastases. Genes relevant for BCC development were analyzed in tumor and metastasis material with small molecule molecular inversion probes (smMIPs) for PTCH1, PTCH2, SMO, SUFU, GLI2, and TP53 or with targeted next generation sequencing of the same genes and CDKN2A, CDKN2B, CIC, DAXX, DDX3X, FUBP1, NF1, NF2, PTEN, SETD2, TRAF7, and the TERT promoter., Results: In 8 of 10 patients, identical gene mutations could be demonstrated in the primary tumors and their metastases. A broad spectrum of mutations was found. Four patients had SMO mutations in their tumor or metastasis, or both. All SMO mutations found were known to cause resistance to targeted therapy with vismodegib., Limitations: In 2 patients there was insufficient qualitative DNA available for genetic analysis., Conclusions: Molecular testing can help to identify the origin of a BCC metastasis and may be of prognostic and therapeutic value., (Copyright © 2019 American Academy of Dermatology, Inc. Published by Elsevier Inc. All rights reserved.)

Background: Vismodegib has been used for the treatment of locally advanced basal cell carcinoma (laBCC) and metastatic BCC (mBCC) since 2011. Most efficacy and safety data are provided by clinical trials. This study evaluates the effectiveness of vismodegib for the treatment of laBCC, mBCC and basal cell nevus syndrome (BCNS) patients, and the tumour characteristics associated with a higher probability of achieving a complete response in the Netherlands., Methods: A retrospective cohort study that included all patients ≥18 years with histologically proven basal cell carcinoma that received ≥1 dose of vismodegib between July 2011 and September 2019 in the Netherlands., Results: In total, 48 laBCC, 11 mBCC and 19 BCNS patients were included. Median progression-free survival was 10.3 months (95% confidence interval (CI), 7.5-22.6) for laBCC, 11.7 (95% CI, 5.2-17.5) for mBCC and 19.1 (95% CI, 7.4-20.2) for BCNS. Larger laBCCs were associated with a lower probability of complete response (hazard ratio (HR) 0.77 per increase in cm, p = 0.02). Of all BCNS patients, 63% received ≥2 treatment sequences with vismodegib; all achieved partial responses., Conclusions: Half of the aBCC patients progress within 1 year after the start of vismodegib treatment. More research is needed to investigate other treatment strategies after vismodegib progression and to evaluate long-term effects of repetitive vismodegib treatment.

Basal cell naevus syndrome (BCNS) is associated with germline mutations in the PTCH1 gene. Postzygotic mosaicism can also cause BCNS. Here we describe two patients, one with multiple basal cell carcinomas (BCCs) and one with clinical BCNS, who had no PTCH1 mutation in DNA extracted from blood. In both patients, we performed genetic analysis on different BCCs, revealing the presence of a shared PTCH1 mutation in all tumours. Our findings show that in patients with symptoms of BCNS and initial absence of a PTCH1 mutation in blood, genetic profiling of BCCs can detect postzygotic mosaicism. What's already known about this topic? Basal cell naevus syndrome (BCNS) is associated with germline mutations in the PTCH1 gene, but it can also be caused by low-grade postzygotic mosaicism in PTCH1. What does this study add? In patients suspected of having BCNS or patients with multiple basal cell carcinomas (BCCs) with a special distribution on the body and no mutation detected in blood, it is worthwhile to search for a shared PTCH1 mutation in their BCCs as this can detect postzygotic mosaicism. This information is important to ensure proper surveillance programmes, choose the right therapy and provide adequate genetic counselling., (© 2018 British Association of Dermatologists.)

Basal cell nevus syndrome (BCNS) is an autosomal dominant disorder most commonly caused by a germline mutation in the PTCH1 gene. PTCH1 is known to have different isoforms with different functional properties and expression patterns among tissues. We detected a novel, pathogenic de novo mutation in PTCH1 isoform 1b (c.114delG) in a BCNS patient. Furthermore, we elucidated the specific expression pattern of PTCH1 isoforms in normal skin, BCC and peripheral blood by studying expression of different PTCH1 isoforms. Human skin showed expression of isoforms 1b and 1d, while peripheral blood additionally showed 1a and 1e expression. BCCs showed expression of all isoforms. Here we report a patient with a novel, isoform 1b specific mutation in PTCH1 and thereby distinguish PTCH1 isoform 1b as the major transcript in the development of BCNS.