Objectives: The distinction of clinically uncertain, poorly differentiated liver masses into primary liver cancer (PLC) of cholangiocytic origin (intrahepatic cholangiocarcinoma; CCA) or hepatocellular origin (hepatocellular carcinoma; HCC) vs. metastasis is highly relevant to guiding patient treatment. Protocols differ in terms of resection, local ablation, liver transplantation, or systemic therapies with immune checkpoint inhibitors (ICIs) and tyrosine kinase inhibitors (TKIs). Methods: This retrospective case series exemplifies a multidisciplinary, practical guide to clinically uncertain liver masses using imaging, histomorphology, immune phenotyping, and mutational testing of telomerase promoter (TERT) combined with a literature review. Results: In 2/3 patients with uncertain liver masses and inconclusive immunohistochemistry profiles, TERT testing supported the diagnosis of poorly differentiated hepatocellular carcinoma. The third case with a history of sclerosing cholangitis and vague adenoid morphology yielded mutations in ARID1a and TP53 and was identified as primary liver cancer, consistent with poorly differentiated intrahepatic cholangiocarcinoma or mixed hepatocellular cholangiocarcinoma (cHCC/CCA). Conclusions: Finding HCC-typical TERT promoter mutations is a useful diagnostic tool in poorly differentiated primary liver cancer.

Vertebrate lonesome kinase (VLK) is the only known extracellular tyrosine kinase, but its physiological functions are largely unknown. We show that VLK is highly expressed in hepatocytes of neonatal mice, but downregulated during adulthood. To determine the role of VLK in liver homeostasis and regeneration, we generated mice with a hepatocyte-specific knockout of the VLK gene (Pkdcc). Cultured progenitor cells established from primary hepatocytes of Pkdcc knockout mice produced a secretome, which promoted their own proliferation in 3D spheroids and proliferation of cultured fibroblasts. In vivo, Pkdcc knockout mice developed liver steatosis with signs of inflammation and perivascular fibrosis upon aging, combined with expansion of liver progenitor cells. In response to chronic CCl4-induced liver injury, the pattern of deposited collagen was significantly altered in these mice. The liver injury marker alpha-fetoprotein (AFP) was increased in the secretome of VLK-deficient cultured progenitor cells and in liver tissues of aged or CCl4-treated knockout mice. These results support a key role for VLK and extracellular protein phosphorylation in liver homeostasis and repair through paracrine control of liver cell function and regulation of appropriate collagen deposition. This article has an associated First Person interview with the first author of the paper.

Transarterial chemoembolization (TACE) is increasingly used in patients with hepatocellular carcinoma (HCC), the most frequent primary liver tumor. Atypical ductular reactions (aDRs) challenge the histological diagnosis in specimens of patients after embolization treatment, mimicking intrahepatic cholangiocarcinoma (CCA) or combined hepatocellular carcinoma-cholangiocarcinoma (HCC-CCA). We characterized aDRs in patients with HCC after embolization treatment in association with therapy mode, response, and survival using histomorphology and spatial microdissection. This retrospective, single-center, longitudinal cohort study included 188 patients with HCC. We compared a study group (n = 105 patients with a total of 206 tumor nodules) vs a treatment-naïve control group (n = 83/112 nodules). The presence of embolization compounds, the type of embolization treatment, tumor necrosis, morphology, and the expression of biliary markers (CK7/19, SOX9) were assessed on whole slides and a tissue microarray using machine-learning-assisted marker profiling. Spatial microdissection and sequencing with the Oncomine Comprehensive Assay (version 3) tested genetic landscapes. The relative risk for aDRs was increased in patients with HCC following embolization therapy compared with the control group (relative risk, 3.6; P < .05). Morphology appears as ribbon-like with atypical, confluent ducts usually found on the interface of necrosis and vital tumor nodules. Strong intensity of CK7/19 and SOX9 was observed throughout, compared with a heterogenous expression pattern in combined HCC-CCA. Spatial microdissection of aDRs showed variants of unknown significance in 1 of 13 cases (NTRK3) but no CCA-typical mutations. In contrast, combined HCC-CCA (n = 4) displayed oncogene alterations in known targets (TP53, BAP1, and TERT). Increased aDRs in specimens of patients with HCC after transarterial embolization treatment can be identified as regenerative phenomenon with distinct morphology and immunophenotype.

Introduction: During routine examination of specimens from patients with steatotic liver disease (SLD), we repeatedly observed a peculiar phenomenon characterized by obstruction of the hepatic sinusoids by lipid vacuoles (lipidic obstruction of sinusoids, LOS). These changes were reminiscent of pseudopeliotic steatosis (PPS), a complication following liver transplantation (LT), but notably occurred outside this context. The aim of our study was to identify diagnostic indicators for LOS and to determine its clinical significance. Methods: Liver specimens routinely sent to our institute between 2019 and 2024 with SLD were examined for LOS. The extracellular nature of the fat and the compression of the sinusoids were demonstrated by ancillary stains (Gomori, CD68, collagen IV). The extent of the LOS was quantified by measuring the area and maximum diameter of fat lakes. The clinical course of patients with LOS was retrospectively evaluated and correlated with the histological findings. Results: LOS was observed in eight patients, ranging from focal to very extensive extracellular fat. The diagnosis was based on routine histology, supplemented by collagen IV stain highlighting double contours of sinusoids. The morphological findings suggested that lipidic obstruction of the hepatic sinusoids was a key pathophysiological factor. LOS was associated with liver necrosis and activation of macrophages. Patients with LOS exhibited a variable clinical course, ranging from subclinical to severe, including LT or even death. The extent of fat lakes correlated with the severity of the clinical course. Conclusions: We suggest the term LOS for a particular pattern of liver damage that can occur in SLD outside the transplantation setting and may lead to impaired hepatic blood flow. LOS is associated with a variable clinical presentation, ranging from subclinical to fatal. Clinicians and pathologists should be aware of this complication of SLD, which is diagnosed by liver histology.