The anatomic basis of leptomeningeal metastasis.

Leptomeningeal metastasis (LM), or spread of cancer to the cerebrospinal fluid (CSF)-filled space surrounding the central nervous system, is a fatal complication of cancer. Entry into this space poses an anatomical challenge for cancer cells; movement of cells between the blood and CSF is tightly regulated by the blood-CSF barriers. Anatomical understanding of the leptomeninges provides a roadmap of corridors for cancer entry. This Review describes the anatomy of the leptomeninges and routes of cancer spread to the CSF. Granular understanding of LM by route of entry may inform strategies for novel diagnostic and preventive strategies as well as therapies.

Very low-dose radiotherapy for extranodal marginal zone lymphoma of bronchus-associated lymphoid tissue.

Extranodal marginal zone lymphoma of bronchus-associated lymphoid tissue (BALT) is a rare cancer for which optimal treatment strategies are undefined. Retrospective analyses suggest excellent outcomes with surgical resection for localized BALT lymphoma; however, the role of radiotherapy remains underexplored. We report the largest-to-date single-center analysis of 13 primary BALT lymphoma patients treated with radiotherapy. Of 15 treated lesions, we report a 100% response rate with complete response (CR) achieved in 67% of lesions. Among 10 lesions treated with very low-dose radiotherapy (VLDRT; 4 Gray [Gy]), 6 (60%) achieved a CR; among 5 lesions treated with full-dose radiotherapy (24-36 Gy), 4 (80%) achieved a CR. There were no local recurrences. Only one patient, treated with 30 Gy, developed an acute grade 3/4 toxic effect. There were no events of radiation-induced secondary malignancies. Our institutional experience indicates that radiotherapy, including VLDRT, is a safe and effective treatment for primary BALT lymphoma.

Early Detection of Leptomeningeal Metastases Among Patients Undergoing Spinal Stereotactic Radiosurgery.

Purpose: The management of patients with advanced solid malignancies increasingly uses stereotactic body radiation therapy (SBRT). Advanced cancer patients are at risk for developing leptomeningeal metastasis (LM), a fatal complication of metastatic cancer. Cerebrospinal fluid (CSF) is routinely collected during computed tomography (CT) myelography for spinal SBRT planning, offering an opportunity for early LM detection by CSF cytology in the absence of radiographic LM or LM symptoms (subclinical LM). This study tested the hypothesis that early detection of tumor cells in CSF in patients undergoing spine SBRT portends a similarly poor prognosis compared with clinically overt LM. Methods and Materials: We retrospectively analyzed clinical records for 495 patients with metastatic solid tumors who underwent CT myelography for spinal SBRT planning at a single institution from 2014 to 2019. Results: Among patients planned for SBRT, 51 (10.3%) developed LM. Eight patients (1.6%) had subclinical LM. Median survival with LM was similar between patients with subclinical versus clinically evident LM (3.6 vs 3.0 months, P = .30). Patients harboring both parenchymal brain metastases and LM (29/51) demonstrated shorter survival than those with LM alone (2.4 vs 7.1 months, P = .02). Conclusions: LM remains a fatal complication of metastatic cancer. Subclinical LM detected by CSF cytology in spine SBRT patients has a similarly poor prognosis compared with standardly detected LM and warrants consideration of central nervous system-directed therapies. As aggressive local therapies are increasingly used for metastatic patients, more sensitive CSF evaluation may further identify patients with subclinical LM and should be evaluated prospectively.

Neurochemically and Hodologically Distinct Ascending VGLUT3 versus Serotonin Subsystems Comprise the r2-Pet1 Median Raphe.

Brainstem median raphe (MR) neurons expressing the serotonergic regulator gene Pet1 send collateralized projections to forebrain regions to modulate affective, memory-related, and circadian behaviors. Some Pet1 neurons express a surprisingly incomplete battery of serotonin pathway genes, with somata lacking transcripts for tryptophan hydroxylase 2 (Tph2) encoding the rate-limiting enzyme for serotonin [5-hydroxytryptamine (5-HT)] synthesis, but abundant for vesicular glutamate transporter type 3 (Vglut3) encoding a synaptic vesicle-associated glutamate transporter. Genetic fate maps show these nonclassical, putatively glutamatergic Pet1 neurons in the MR arise embryonically from the same progenitor cell compartment-hindbrain rhombomere 2 (r2)-as serotonergic TPH2+ MR Pet1 neurons. Well established is the distribution of efferents en masse from r2-derived, Pet1-neurons; unknown is the relationship between these efferent targets and the specific constituent source-neuron subgroups identified as r2-Pet1Tph2-high versus r2-Pet1Vglut3-high Using male and female mice, we found r2-Pet1 axonal boutons segregated anatomically largely by serotonin+ versus VGLUT3+ identity. The former present in the suprachiasmatic nucleus, paraventricular nucleus of the thalamus, and olfactory bulb; the latter are found in the hippocampus, cortex, and septum. Thus r2-Pet1Tph2-high and r2-Pet1Vglut3-high neurons likely regulate distinct brain regions and behaviors. Some r2-Pet1 boutons encased interneuron somata, forming specialized presynaptic "baskets" of VGLUT3+ or VGLUT3+/5-HT+ identity; this suggests that some r2-Pet1Vglut3-high neurons may regulate local networks, perhaps with differential kinetics via glutamate versus serotonin signaling. Fibers from other Pet1 neurons (non-r2-derived) were observed in many of these same baskets, suggesting multifaceted regulation. Collectively, these findings inform brain organization and new circuit nodes for therapeutic considerations.SIGNIFICANCE STATEMENT Our findings match axonal bouton neurochemical identity with distant cell bodies in the brainstem raphe. The results are significant because they suggest that disparate neuronal subsystems derive from Pet1+ precursor cells of the embryonic progenitor compartment rhombomere 2 (r2). Of these r2-Pet1 neuronal subsystems, one appears largely serotonergic, as expected given expression of the serotonergic regulator PET1, and projects to the olfactory bulb, thalamus, and suprachiasmatic nucleus. Another expresses VGLUT3, suggesting principally glutamate transmission, and projects to the hippocampus, septum, and cortex. Some r2-Pet1 boutons-those that are VGLUT3+ or VGLUT3+/5-HT+ co-positive-comprise "baskets" encasing interneurons, suggesting that they control local networks perhaps with differential kinetics via glutamate versus serotonin signaling. Results inform brain organization and circuit nodes for therapeutic consideration.

Patterns of Failure and the Need for Biliary Intervention in Resected Biliary Tract Cancers After Chemoradiation.

BACKGROUND: This study assessed patterns of failure and rates of subsequent biliary intervention among patients with resected biliary tract cancers (BTCs) including gallbladder carcinoma (GBC) and extra- and intrahepatic cholangiocarcinoma (eCCA and iCCA) treated with adjuvant chemoradiation therapy (CRT). METHODS: In this single-institution retrospective analysis of 80 patients who had GBC (n = 29), eCCA (n = 43), or iCCA (n = 8) treated with curative-intent resection and adjuvant CRT from 2007 to 2017, the median radiation dose was 50.4 Gy (range 36-65 Gy) with concurrent 5-fluorouracil (5-FU) chemotherapy. All but two of the patients received adjuvant chemotherapy. The 2-year locoregional failure (LRF), 2-year recurrence-free survival (RFS), and 2-year overall survival (OS), and univariate predictors of LRF, RFS, and OS were calculated for the entire cohort and for a subgroup excluding patients with iCCA (n = 72). The predictors of biliary interventions also were assessed. RESULTS: Of the 80 patients (median follow-up period, 30.5 months; median OS, 33.9 months), 54.4% had American Joint Committee on Cancer (AJCC) stage 1 or 2 disease, 57.1% were lymph node-positive, and 66.3% underwent margin-negative resection. For the entire cohort, 2-year LRF was 23.8%, 2-year RFS was  43.7%, and 2-year OS was 62.1%.  When patients with iCCA were excluded, the 2-year LRF was 22.6%, the 2-year RFS was 43.9%, and the 2-year OS was 59.2%. In the overall and subgroup univariate analyses, lymph node positivity was associated with greater LRF, whereas resection margin was not. Biliary intervention was required for 12 (63.2%) of the 19 patients with LRF versus 11 (18%) of the 61 patients without LRF (P < 0.001). Of the 12 patients with LRF who required biliary intervention, 4 died of biliary complications. CONCLUSIONS: The LRF rates remained significant despite adjuvant CRT. Lymph node positivity may be associated with increased risk of LRF. Positive margins were not associated with greater LRF, suggesting that CRT may mitigate LRF risk for this group. An association between LRF and higher rates of subsequent biliary interventions was observed, which may yield significant morbidity. Novel strategies to decrease the rates of LRF should be considered.

Assessment and Treatment Outcomes of Persistent Radiation-Induced Alopecia in Patients With Cancer.

Importance: Persistent radiation-induced alopecia (pRIA) and its management have not been systematically described. Objective: To characterize pRIA in patients with primary central nervous system (CNS) tumors or head and neck sarcoma. Design, Setting, and Participants: A retrospective cohort study of patients from January 1, 2011, to January 30, 2019, was conducted at 2 large tertiary care hospitals and comprehensive cancer centers. Seventy-one children and adults diagnosed with primary CNS tumors or head and neck sarcomas were evaluated for pRIA. Main Outcomes and Measures: The clinical and trichoscopic features, scalp radiation dose-response relationship, and response to topical minoxidil were assessed using standardized clinical photographs of the scalp, trichoscopic images, and radiotherapy treatment plans. Results: Of the 71 patients included (median [range] age, 27 [4-75] years; 51 female [72%]), 64 (90%) had a CNS tumor and 7 (10%) had head and neck sarcoma. Alopecia severity was grade 1 in 40 of 70 patients (56%), with localized (29 of 54 [54%]), diffuse (13 of 54 [24%]), or mixed (12 of 54 [22%]) patterns. The median (range) estimated scalp radiation dose was 39.6 (15.1-50.0) Gy; higher dose (odds ratio [OR], 1.15; 95% CI, 1.04-1.28) and proton irradiation (OR, 5.7; 95% CI, 1.05-30.8) were associated with greater alopecia severity (P < .001), and the dose at which 50% of patients were estimated to have severe (grade 2) alopecia was 36.1 Gy (95% CI, 33.7-39.6 Gy). Predominant trichoscopic features included white patches (16 of 28 [57%]); in 15 patients, hair-shaft caliber negatively correlated with scalp dose (correlation coefficient, -0.624; P = .01). The association between hair density and scalp radiation dose was not statistically significant (-0.381; P = .16). Twenty-eight of 34 patients (82%) responded to topical minoxidil, 5% (median follow-up, 61 [interquartile range, 21-105] weeks); 4 of 25 (16%) topical minoxidil recipients with clinical images improved in severity grade. Two patients responded to hair transplantation and 1 patient responded to plastic surgical reconstruction. Conclusions and Relevance: Persistent radiation-induced alopecia among patients with primary CNS tumors or head and neck sarcomas represents a dose-dependent phenomenon that has distinctive clinical and trichoscopic features. The findings of this study suggest that topical minoxidil and procedural interventions may have benefit in the treatment of pRIA.

Insights into optic pathway glioma vision loss from mouse models of neurofibromatosis type 1.

Neurofibromatosis type 1 (NF1) is a common cancer predisposition syndrome caused by mutations in the NF1 gene. The NF1-encoded protein (neurofibromin) is an inhibitor of the oncoprotein RAS and controls cell growth and survival. Individuals with NF1 are prone to developing low-grade tumors of the optic nerves, chiasm, tracts, and radiations, termed optic pathway gliomas (OPGs), which can cause vision loss. A paucity of surgical tumor specimens and of patient-derived xenografts for investigative studies has limited our understanding of human NF1-associated OPG (NF1-OPG). However, mice genetically engineered to harbor Nf1 gene mutations develop optic gliomas that share many features of their human counterparts. These genetically engineered mouse (GEM) strains have provided important insights into the cellular and molecular determinants that underlie mouse Nf1 optic glioma development, maintenance, and associated vision loss, with relevance by extension to human NF1-OPG disease. Herein, we review our current understanding of NF1-OPG pathobiology and describe the mechanisms responsible for tumor initiation, growth, and associated vision loss in Nf1 GEM models. We also discuss how Nf1 GEM and other preclinical models can be deployed to identify and evaluate molecularly targeted therapies for OPG, particularly as they pertain to future strategies aimed at preventing or improving tumor-associated vision loss in children with NF1.

Multi-Scale Molecular Deconstruction of the Serotonin Neuron System.

Serotonergic (5HT) neurons modulate diverse behaviors and physiology and are implicated in distinct clinical disorders. Corresponding diversity in 5HT neuronal phenotypes is becoming apparent and is likely rooted in molecular differences, yet a comprehensive approach characterizing molecular variation across the 5HT system is lacking, as is concomitant linkage to cellular phenotypes. Here we combine intersectional fate mapping, neuron sorting, and genome-wide RNA-seq to deconstruct the mouse 5HT system at multiple levels of granularity-from anatomy, to genetic sublineages, to single neurons. Our unbiased analyses reveal principles underlying system organization, 5HT neuron subtypes, constellations of differentially expressed genes distinguishing subtypes, and predictions of subtype-specific functions. Using electrophysiology, subtype-specific neuron silencing, and conditional gene knockout, we show that these molecularly defined 5HT neuron subtypes are functionally distinct. Collectively, this resource classifies molecular diversity across the 5HT system and discovers sertonergic subtypes, markers, organizing principles, and subtype-specific functions with potential disease relevance.

Hedgehog-responsive candidate cell of origin for diffuse intrinsic pontine glioma.

Diffuse intrinsic pontine gliomas (DIPGs) are highly aggressive tumors of childhood that are almost universally fatal. Our understanding of this devastating cancer is limited by a dearth of available tissue for study and by the lack of a faithful animal model. Intriguingly, DIPGs are restricted to the ventral pons and occur during a narrow window of middle childhood, suggesting dysregulation of a postnatal neurodevelopmental process. Here, we report the identification of a previously undescribed population of immunophenotypic neural precursor cells in the human and murine brainstem whose temporal and spatial distributions correlate closely with the incidence of DIPG and highlight a candidate cell of origin. Using early postmortem DIPG tumor tissue, we have established in vitro and xenograft models and find that the Hedgehog (Hh) signaling pathway implicated in many developmental and oncogenic processes is active in DIPG tumor cells. Modulation of Hh pathway activity has functional consequences for DIPG self-renewal capacity in neurosphere culture. The Hh pathway also appears to be active in normal ventral pontine precursor-like cells of the mouse, and unregulated pathway activity results in hypertrophy of the ventral pons. Together, these findings provide a foundation for understanding the cellular and molecular origins of DIPG, and suggest that the Hh pathway represents a potential therapeutic target in this devastating pediatric tumor.