Gastrointestinal stromal tumors (GISTs) are malignant mesenchymal tumors arising from the intestinal pacemaker cells of Cajal. They compose a heterogenous group of tumors due to a variety of molecular alterations. The most common gain-of-function mutations in GISTs are either in the KIT (60–70%) or platelet-derived growth factor receptor alpha (PDGFRA) genes (10–15%), which are mutually exclusive. However, a smaller subset, lacking KIT and PDGFRA mutations, is considered wild-type GISTs and presents distinct molecular findings with the activation of different proliferative pathways, structural chromosomal and epigenetic changes, such as inactivation of the NF1 gene, mutations in the succinate dehydrogenase (SDH), BRAF, and RAS genes, and also NTRK fusions. Currently, a molecular evaluation of GISTs is imperative in many scenarios, aiding in treatment decisions from the (neo)adjuvant to the metastatic setting. Here, we review the most recent data on the molecular profile of GISTs and highlight therapeutic implications according to distinct GIST molecular subtypes.

Squamous cell carcinoma of the anal canal (SCCA) is a rare neoplasm, but with rising incidence rates in the past few decades; it is etiologically linked with the human papillomavirus (HPV) infection and is especially prevalent in immunocompromised patients, mainly those infected with HIV. Fluoropyrimidine-based chemoradiotherapy remains the cornerstone of the treatment of non-metastatic disease, but the locally advanced disease still presents high rates of disease recurrence and systemic therapy of SCCA is an unmet clinical need. Despite sharing common molecular aspects with other HPV-related malignancies, such as cervical and head and neck cancers, SCCA presents specific epigenomic, genomic, and transcriptomic abnormalities, which suggest that genome-guided personalized therapies should be specifically designed for this disease. Actionable mutations are rare in SCCA and immune checkpoint inhibition has not yet been proven useful in an unselected population of patients. Therefore, advances in systemic therapy of SCCA will only be possible with the identification of predictive biomarkers and the subsequent development of targeted therapies or immunotherapeutic approaches that consider the unique tumor microenvironment and the intra- and inter-tumoral heterogeneity. In the present review, we address the molecular characterization of SCCA and discuss potential diagnostic, predictive and prognostic biomarkers of this complex and challenging disease.

Background and Objective Immune checkpoint inhibition has shed light on a new era in cancer therapy, and randomized clinical trials have demonstrated that a meaningful portion of the overall population of metastatic gastric cancer (GC) patients may derive clinical benefit from immunotherapy, which raises the relevance in identifying predictive biomarkers. Programmed cell death-ligand 1 (PD-L1) expression has demonstrated a significant association between level of expression and the magnitude of benefit derived from immune checkpoint inhibition in GC. Nevertheless, this biomarker shows several pitfalls that must be considered in the therapeutic decision to incorporate immune checkpoint inhibition as the standard of care of GC, such as spatial and temporal heterogeneity, interobserver variability, immunohistochemistry (IHC) assay, and influence by chemotherapy or radiation therapy. Methods In the present comprehensive review, we revised the main studies regarding PD-L1 evaluation in GC. Key Content and Findings Here we describe the molecular characteristics of the tumor microenvironment in GC, the obstacles in the interpretation of PD-L1 expression and present the data of the clinical trials that have evaluated the efficacy and safety of immune checkpoint inhibition and the association with the biomarker expression, both in first-line and later lines of therapy. Conclusions From the emerging predictive biomarkers for immune checkpoint inhibition, PD-L1 has demonstrated a meaningful association between level of expression in tumor microenvironment and the magnitude of benefit derived from immune checkpoint inhibition in GC.

This mutation is the first of its kind described in chondrosarcoma, serving as an identifying marker of chondroid differentiation, and becoming the first molecular target with potential anticancer effect, translating into the development of therapies targeting these mutations currently being tested further in preclinical models and clinical trials.