Lymphatic Invasion of Plakoglobin-Dependent Tumor Cell Clusters Drives Formation of Polyclonal Lung Metastases in Colon Cancer.

BACKGROUND & AIMS: Patients with colon cancer with liver metastases may be cured with surgery, but the presence of additional lung metastases often precludes curative treatment. Little is known about the processes driving lung metastasis. This study aimed to elucidate the mechanisms governing lung vs liver metastasis formation. METHODS: Patient-derived organoid (PDO) cultures were established from colon tumors with distinct patterns of metastasis. Mouse models recapitulating metastatic organotropism were created by implanting PDOs into the cecum wall. Optical barcoding was applied to trace the origin and clonal composition of liver and lung metastases. RNA sequencing and immunohistochemistry were used to identify candidate determinants of metastatic organotropism. Genetic, pharmacologic, in vitro, and in vivo modeling strategies identified essential steps in lung metastasis formation. Validation was performed by analyzing patient-derived tissues. RESULTS: Cecum transplantation of 3 distinct PDOs yielded models with distinct metastatic organotropism: liver only, lung only, and liver and lung. Liver metastases were seeded by single cells derived from select clones. Lung metastases were seeded by polyclonal clusters of tumor cells entering the lymphatic vasculature with very limited clonal selection. Lung-specific metastasis was associated with high expression of desmosome markers, including plakoglobin. Plakoglobin deletion abrogated tumor cell cluster formation, lymphatic invasion, and lung metastasis formation. Pharmacologic inhibition of lymphangiogenesis attenuated lung metastasis formation. Primary human colon, rectum, esophagus, and stomach tumors with lung metastases had a higher N-stage and more plakoglobin-expressing intra-lymphatic tumor cell clusters than those without lung metastases. CONCLUSIONS: Lung and liver metastasis formation are fundamentally distinct processes with different evolutionary bottlenecks, seeding entities, and anatomic routing. Polyclonal lung metastases originate from plakoglobin-dependent tumor cell clusters entering the lymphatic vasculature at the primary tumor site.

Reclassification of Appendiceal Mucinous Neoplasms and Associated Pseudomyxoma Peritonei According to the Peritoneal Surface Oncology Group International Consensus: Clinicopathological Reflections of a Two-Center Cohort Study.

BACKGROUND: International consensus on classifications of appendiceal mucinous neoplasms (AMNs) and associated pseudomyxoma peritonei (PMP) have been carefully made but clinicopathological associations supporting decision making remain scarce. OBJECTIVE: This study aimed to assess interdependence between AMNs and PMP and provide directions for clinical management. METHODS: This two-center retrospective cohort study reviewed patients with PMP treated with cytoreductive surgery and hyperthermic intraperitoneal chemotherapy between 2005 and 2021. The primary objective was to reassess histopathologic grade of AMNs and PMP according to the Peritoneal Surface Oncology Group International classification and to establish its interdependence. Secondary outcomes were recurrence rate, PMP grade progression, ovarian involvement, and overall survival (OS). RESULTS: Of 105 patients included, 78 (74.3%) had low-grade AMNs as the primary tumor, 8 (7.6%) had high-grade AMNs, 7 (6.7%) had mucinous adenocarcinoma (MAC), 1 (0.9%) had MAC with signet ring cells (SRC), and 11 (10.5%) had unidentified tumors. Overall, 11 patients (10.5%) had no PMP, 21 (20.0%) had acellular mucin, 56 (53.3%) had low-grade PMP, 12 (11.4%) had high-grade PMP, and 5 (4.8%) had PMP-SRC. In 11 cases (13.3%), AMNs and matching PMP grade differed. Over a 16-year follow-up, recurrence occurred in 31.8%, with three cases showing histopathologically changed PMP. Ovarian involvement was observed in 43/65 females (66.2%). Median OS was 13.8 years, and 5-year OS rates were 100%, 74.4%, 44.4%, and 20% for acellular mucin, low-grade PMP, high-grade PMP and PMP-SRC, respectively (p < 0.001). CONCLUSIONS: AMN histology does not always reflects its associated PMP grade, while PMP grade strongly influences survival. Ovarian involvement and recurrent PMP showing unchanged histopathological features are common.

Peritoneal metastases from colorectal cancer belong to Consensus Molecular Subtype 4 and are sensitised to oxaliplatin by inhibiting reducing capacity.

BACKGROUND: Peritoneal metastases (PM) in colorectal cancer (CRC) are associated with therapy resistance and poor survival. Oxaliplatin monotherapy is widely applied in the intraperitoneal treatment of PM, but fails to yield clinical benefit. We aimed to identify the mechanism(s) underlying PM resistance to oxaliplatin and to develop strategies overcoming such resistance. EXPERIMENTAL DESIGN: We generated a biobank consisting of 35 primary tumour regions and 59 paired PM from 12 patients. All samples were analysed by RNA sequencing. We also generated a series of PM-derived organoid (PMDO) cultures and used these to design and test strategies to overcome resistance to oxaliplatin. RESULTS: PM displayed various hallmarks of aggressive CRC biology. The vast majority of PM and paired primary tumours belonged to the Consensus Molecular Subtype 4 (CMS4). PMDO cultures were resistant to oxaliplatin and expressed high levels of glutamate-cysteine ligase (GCLC) causing detoxification of oxaliplatin through glutathione synthesis. Genetic or pharmacological targeting of GCLC sensitised PMDOs to a 1-h exposure to oxaliplatin, through increased platinum-DNA adduct formation. CONCLUSIONS: These results link oxaliplatin resistance of colorectal PM to their CMS4 status and high reducing capacity. Inhibiting the reducing capacity of PM may be an effective strategy to overcome PM resistance to oxaliplatin.

Patient-reported outcomes during repetitive oxaliplatin-based pressurized intraperitoneal aerosol chemotherapy for isolated unresectable colorectal peritoneal metastases in a multicenter, single-arm, phase 2 trial (CRC-PIPAC).

BACKGROUND: CRC-PIPAC prospectively assessed repetitive oxaliplatin-based pressurized intraperitoneal aerosol chemotherapy (PIPAC-OX) as a palliative monotherapy (i.e., without concomitant systemic therapy in between subsequent procedures) for unresectable colorectal peritoneal metastases (CPM). The present study explored patient-reported outcomes (PROs) during trial treatment. METHODS: In this single-arm phase 2 trial in two tertiary centers, patients with isolated unresectable CPM received 6-weekly PIPAC-OX (92 mg/m2). PROs (calculated from EQ-5D-5L, and EORTC QLQ-C30 and QLQ-CR29) were compared between baseline and 1 and 4 weeks after the first three procedures using linear mixed modeling with determination of clinical relevance (Cohen's D ≥ 0.50) of statistically significant differences. RESULTS: Twenty patients underwent 59 procedures (median 3 [range 1-6]). Several PROs solely worsened 1 week after the first procedure (index value - 0.10, p < 0.001; physical functioning - 20, p < 0.001; role functioning - 27, p < 0.001; social functioning - 18, p < 0.001; C30 summary score - 16, p < 0.001; appetite loss + 15, p = 0.007; diarrhea + 15, p = 0.002; urinary frequency + 13, p = 0.004; flatulence + 13, p = 0.001). These PROs returned to baseline at subsequent time points. Other PROs worsened 1 week after the first procedure (fatigue + 23, p < 0.001; pain + 29, p < 0.001; abdominal pain + 32, p < 0.001), second procedure (fatigue + 20, p < 0.001; pain + 21, p < 0.001; abdominal pain + 20, p = 0.002), and third procedure (pain + 22, p < 0.001; abdominal pain + 22, p = 0.002). Except for appetite loss, all changes were clinically relevant. All analyzed PROs returned to baseline 4 weeks after the third procedure. CONCLUSIONS: Patients receiving repetitive PIPAC-OX monotherapy for unresectable CPM had clinically relevant but reversible worsening of several PROs, mainly 1 week after the first procedure. TRIAL REGISTRATION: Clinicaltrials.gov: NCT03246321; Netherlands trial register: NL6426.

Pressurized Intraperitoneal Aerosol Chemotherapy (Oxaliplatin) for Unresectable Colorectal Peritoneal Metastases: A Multicenter, Single-Arm, Phase II Trial (CRC-PIPAC).

BACKGROUND: Despite its increasing use, pressurized intraperitoneal aerosol chemotherapy with oxaliplatin (PIPAC-OX) has never been prospectively investigated as a palliative monotherapy for colorectal peritoneal metastases in clinical trials. This trial aimed to assess the safety (primary aim) and antitumor activity (key secondary aim) of PIPAC-OX monotherapy in patients with unresectable colorectal peritoneal metastases. METHODS: In this two-center, single-arm, phase II trial, patients with isolated unresectable colorectal peritoneal metastases in any line of palliative treatment underwent 6-weekly PIPAC-OX (92 mg/m2). Key outcomes were major treatment-related adverse events (primary outcome), minor treatment-related adverse events, hospital stay, tumor response (radiological, biochemical, pathological, ascites), progression-free survival, and overall survival. RESULTS: Twenty enrolled patients underwent 59 (median 3, range 1-6) PIPAC-OX procedures. Major treatment-related adverse events occurred in 3 of 20 (15%) patients after 5 of 59 (8%) procedures (abdominal pain, intraperitoneal hemorrhage, iatrogenic pneumothorax, transient liver toxicity), including one possibly treatment-related death (sepsis of unknown origin). Minor treatment-related adverse events occurred in all patients after 57 of 59 (97%) procedures, the most common being abdominal pain (all patients after 88% of procedures) and nausea (65% of patients after 39% of procedures). Median hospital stay was 1 day (range 0-3). Response rates were 0% (radiological), 50% (biochemical), 56% (pathological), and 56% (ascites). Median progression-free and overall survival were 3.5 months (interquartile range [IQR] 2.5-5.7) and 8.0 months (IQR 6.3-12.6), respectively. CONCLUSIONS: In patients with unresectable colorectal peritoneal metastases undergoing PIPAC-OX monotherapy, some major adverse events occurred and minor adverse events were common. The clinical relevance of observed biochemical, pathological, and ascites responses remains to be determined, especially since radiological response was absent.

Systemic Pharmacokinetics of Oxaliplatin After Intraperitoneal Administration by Electrostatic Pressurized Intraperitoneal Aerosol Chemotherapy (ePIPAC) in Patients with Unresectable Colorectal Peritoneal Metastases in the CRC-PIPAC Trial.

BACKGROUND: Electrostatic pressurized intraperitoneal aerosol chemotherapy (ePIPAC) is a palliative treatment for unresectable peritoneal metastases from various primary cancers. However, little is known about the systemic pharmacokinetics of oxaliplatin after ePIPAC. METHODS: Twenty patients with unresectable colorectal peritoneal metastases were treated with repetitive ePIPAC monotherapy with oxaliplatin (92 mg/m2) and a simultaneous intravenous bolus of leucovorin (20 mg/m2) and 5-fluorouracil (400 mg/m2). Samples were collected during each ePIPAC: whole blood at t = 0, t = 5, t = 10, t = 20, t = 30, t = 60, t = 120, t = 240, t = 360 and t = 1080 min for plasma and plasma ultrafiltrate concentrations; urine at t = 0, t = 1, t = 3, t = 5 and t = 7 days. Samples were analyzed using atomic absorption spectrometry. Pharmacokinetics were analyzed using nonlinear mixed-effects modeling. RESULTS: Four patients received one ePIPAC, three patients received two ePIPAC, and thirteen patients received ≥ 3 ePIPAC. The population pharmacokinetic models adequately described the pharmacokinetics of oxaliplatin after ePIPAC. The plasma ultrafiltrate Cmax of oxaliplatin reached 1.36-1.90 µg/mL after 30 min with an AUC0-24 h of 9.6-11.7 µg/mL * h. The plasma Cmax reached 2.67-3.28 µg/mL after 90 min with an AUC0-24 h of 49.0-59.5 µg/mL * h. The absorption rate constant (Ka) was 1.13/h. Urine concentrations of oxaliplatin rapidly decreased to less than 3.60 µg/mL in 90% of the samples at day 7. DISCUSSION: Systemic exposure to oxaliplatin after ePIPAC seemed comparable to that after systemic chemotherapy, as described in other literature. Since this is an indirect comparison, future research should focus on the direct comparison between the systemic exposure to oxaliplatin after ePIPAC and after systemic chemotherapy. TRIAL REGISTRATION: NCT03246321, Pre-results; ISRCTN89947480, Pre-results; NTR6603, Pre-results; EudraCT: 2017-000927-29, Pre-results.

Tumor characteristics and clinical outcome of peritoneal metastasis of gastric origin treated with a hyperthermic intraperitoneal chemotherapy procedure in the PERISCOPE I trial.

INTRODUCTION: The PERISCOPE I (Treatment of PERItoneal dissemination in Stomach Cancer patients with cytOreductive surgery and hyPErthermic intraperitoneal chemotherapy) study was conducted to investigate the safety and feasibility of hyperthermic intraperitoneal chemotherapy (HIPEC) in gastric cancer patients with limited peritoneal dissemination. In this study, tumor characteristics and clinical outcome of the patients treated in the PERISCOPE I trial were investigated. METHODS: Patients who had undergone the full study protocol were selected; that is, preoperative systemic chemotherapy, followed by a surgical procedure consisting of a (sub)total gastrectomy, cytoreductive surgery, and HIPEC with oxaliplatin (460 mg/m2 ) and docetaxel (in escalating doses). RESULTS: Twenty-five PERISCOPE I patients underwent the full study protocol. Most patients had an ypT3-4 tumor (96%) and the diffuse-type histology was predominant (64%). Seven patients (28%) had a microscopically irradical (R1) resection. In all patients, a complete cytoreduction was achieved. Median follow-up was 37 (95% confidence interval [CI]: 34-39) months. Disease recurrence was detected in 17 patients (68%). Median disease-free and overall survival were 12 and 15 months, respectively. CONCLUSION: In this series of gastric cancer patients with limited peritoneal dissemination who underwent HIPEC surgery, unfavorable tumor characteristics were common. Survival might be encouraging but disease recurrence was frequent. The efficacy of an HIPEC procedure in improving prognosis is currently being investigated in the PERISCOPE II trial.

Perioperative systemic therapy and cytoreductive surgery with HIPEC versus upfront cytoreductive surgery with HIPEC alone for isolated resectable colorectal peritoneal metastases: protocol of a multicentre, open-label, parallel-group, phase II-III, randomised, superiority study (CAIRO6)

BACKGROUND: Upfront cytoreductive surgery with HIPEC (CRS-HIPEC) is the standard treatment for isolated resectable colorectal peritoneal metastases (PM) in the Netherlands. This study investigates whether addition of perioperative systemic therapy to CRS-HIPEC improves oncological outcomes. METHODS: This open-label, parallel-group, phase II-III, randomised, superiority study is performed in nine Dutch tertiary referral centres. Eligible patients are adults who have a good performance status, histologically or cytologically proven resectable PM of a colorectal adenocarcinoma, no systemic colorectal metastases, no systemic therapy for colorectal cancer within six months prior to enrolment, and no previous CRS-HIPEC. Eligible patients are randomised (1:1) to perioperative systemic therapy and CRS-HIPEC (experimental arm) or upfront CRS-HIPEC alone (control arm) by using central randomisation software with minimisation stratified by a peritoneal cancer index of 0-10 or 11-20, metachronous or synchronous PM, previous systemic therapy for colorectal cancer, and HIPEC with oxaliplatin or mitomycin C. At the treating physician's discretion, perioperative systemic therapy consists of either four 3-weekly neoadjuvant and adjuvant cycles of capecitabine with oxaliplatin (CAPOX), six 2-weekly neoadjuvant and adjuvant cycles of 5-fluorouracil/leucovorin with oxaliplatin (FOLFOX), or six 2-weekly neoadjuvant cycles of 5-fluorouracil/leucovorin with irinotecan (FOLFIRI) followed by four 3-weekly (capecitabine) or six 2-weekly (5-fluorouracil/leucovorin) adjuvant cycles of fluoropyrimidine monotherapy. Bevacizumab is added to the first three (CAPOX) or four (FOLFOX/FOLFIRI) neoadjuvant cycles. The first 80 patients are enrolled in a phase II study to explore the feasibility of accrual and the feasibility, safety, and tolerance of perioperative systemic therapy. If predefined criteria of feasibility and safety are met, the study continues as a phase III study with 3-year overall survival as primary endpoint. A total of 358 patients is needed to detect the hypothesised 15% increase in 3-year overall survival (control arm 50%; experimental arm 65%). Secondary endpoints are surgical characteristics, major postoperative morbidity, progression-free survival, disease-free survival, health-related quality of life, costs, major systemic therapy related toxicity, and objective radiological and histopathological response rates. DISCUSSION: This is the first randomised study that prospectively compares oncological outcomes of perioperative systemic therapy and CRS-HIPEC with upfront CRS-HIPEC alone for isolated resectable colorectal PM. TRIAL REGISTRATION: Clinicaltrials.gov/ NCT02758951 , NTR/ NTR6301 , ISRCTN/ ISRCTN15977568 , EudraCT/ 2016-001865-99 .

Composition of the cellular infiltrate in patients with simple and complex appendicitis.

BACKGROUND: It is now well established that there are two types of appendicitis: simple (nonperforating) and complex (perforating). This study evaluates differences in the composition of the immune cellular infiltrate in children with simple and complex appendicitis. MATERIALS AND METHODS: A total of 47 consecutive children undergoing appendectomy for acute appendicitis between January 2011 and December 2012 were included. Intraoperative criteria were used to identify patients with either simple or complex appendicitis and were confirmed histopathologically. Immune histochemical techniques were used to identify immune cell markers in the appendiceal specimens. Digital imaging analysis was performed using Image J. RESULTS: In the specimens of patients with complex appendicitis, significantly more myeloperoxidase positive cells (neutrophils) (8.7% versus 1.2%, P < 0.001) were detected compared to patients with a simple appendicitis. In contrast, fewer CD8+ T cells (0.4% versus 1.3%, P = 0.016), CD20 + cells (2.9% versus 9.0%, P = 0.027), and CD21 + cells (0.2% versus 0.6%, P = 0.028) were present in tissue from patients with complex compared to simple appendicitis. CONCLUSIONS: The increase in proinflammatory innate cells and decrease of adaptive cells in patients with complex appendicitis suggest potential aggravating processes in complex appendicitis. Further research into the underlying mechanisms may identify novel biomarkers to be able to differentiate simple and complex appendicitis.

First-line palliative systemic therapy alternated with oxaliplatin-based pressurized intraperitoneal aerosol chemotherapy for unresectable colorectal peritoneal metastases: A single-arm phase II trial (CRC-PIPAC-II).

BACKGROUND: Palliative systemic therapy alternated with electrostatic precipitation oxaliplatin-based pressurized intraperitoneal aerosol chemotherapy (ePIPAC) has never been prospectively investigated in patients with unresectable colorectal peritoneal metastases (CPM). The CRC-PIPAC-II study aimed to assess safety, feasibility and efficacy of such bidirectional therapy. METHODS: This two-center, single-arm, phase II trial enrolled chemotherapy-naïve patients to undergo three treatment cycles, consisting of systemic therapy (CAPOX, FOLFOX, FOLFIRI, or FOLFOXIRI, all with bevacizumab) and oxaliplatin-based ePIPAC (92 mg/m2) with intravenous leucovorin (20 mg/m2) and 5-fluorouracil (400 mg/m2). Primary outcome were major treatment-related adverse events. Secondary outcomes included minor events, tumor response, progression-free survival (PFS) and overall survival (OS). RESULTS: Twenty patients completed 52 treatment cycles. Fifteen major events occurred in 7 patients (35 %): 5 events (33 %) related to systemic therapy; 5 (33 %) related to ePIPAC; and 5 (33 %) were biochemical events. No treatment-related deaths occurred. All patients experienced minor events, mostly abdominal pain, nausea and peripheral sensory neuropathy. After treatment, radiological, pathological, cytological, and biochemical response was observed in 0 %, 88 %, 38 %, and 31 % of patients respectively. Curative surgery was achieved in one patient. Median PFS was 10.0 months (95 % confidence interval [CI] 8.0-13.0) and median OS was 17.5 months (95 % CI 13.0-not reached). CONCLUSIONS: Combining palliative systemic therapy with oxaliplatin-based ePIPAC in patients with unresectable CPM was feasible and showed an acceptable safety profile. Treatment-induced response and survival are promising, yet further research is required to determine the additional value of ePIPAC to systemic therapy.

First-line palliative systemic therapy alternated with electrostatic pressurised intraperitoneal aerosol chemotherapy (oxaliplatin) for isolated unresectable colorectal peritoneal metastases: protocol of a multicentre, single-arm, phase II study (CRC-PIPAC-II).

INTRODUCTION: Despite its increasing use, first-line palliative systemic therapy alternated with electrostatic pressurised intraperitoneal aerosol chemotherapy with oxaliplatin (ePIPAC-OX), hereinafter referred to as first-line bidirectional therapy, has never been prospectively investigated in patients with colorectal peritoneal metastases (CPM). As a first step to address this evidence gap, the present study aims to assess the safety, feasibility, antitumour activity, patient-reported outcomes, costs and systemic pharmacokinetics of first-line bidirectional therapy in patients with isolated unresectable CPM. METHODS AND ANALYSIS: In this single-arm, phase II study in two Dutch tertiary referral centres, 20 patients are enrolled. Key eligibility criteria are a good performance status, pathologically proven isolated unresectable CPM, no previous palliative systemic therapy for colorectal cancer, no (neo)adjuvant systemic therapy ≤6 months prior to enrolment and no previous pressurised intraperitoneal aerosol chemotherapy (PIPAC). Patients receive three cycles of bidirectional therapy. Each cycle consists of 6 weeks first-line palliative systemic therapy at the medical oncologists' decision (CAPOX-bevacizumab, FOLFOX-bevacizumab, FOLFIRI-bevacizumab or FOLFOXIRI-bevacizumab) followed by ePIPAC-OX (92 mg/m2) with an intraoperative bolus of intravenous leucovorin (20 mg/m2) and 5-fluorouracil (400 mg/m2). Study treatment ends after the third ePIPAC-OX. The primary outcome is the number of patients with-and procedures leading to-grade ≥3 adverse events (Common Terminology Criteria for Adverse Events V.5.0) up to 4 weeks after the last procedure. Key secondary outcomes include the number of bidirectional cycles in each patient, treatment-related characteristics, grade ≤2 adverse events, tumour response (histopathological, cytological, radiological, biochemical, macroscopic and ascites), patient-reported outcomes, systemic pharmacokinetics of oxaliplatin, costs, progression-free survival and overall survival. ETHICS AND DISSEMINATION: This study is approved by the Dutch competent authority, a medical ethics committee and the institutional review boards of both study centres. Results will be submitted for publication in peer-reviewed medical journals and presented to patients and healthcare professionals. TRIAL REGISTRATION NUMBER: NL8303.

Lymph node metastases develop through a wider evolutionary bottleneck than distant metastases.

Genetic diversity among metastases is poorly understood but contains important information about disease evolution at secondary sites. Here we investigate inter- and intra-lesion heterogeneity for two types of metastases that associate with different clinical outcomes: lymph node and distant organ metastases in human colorectal cancer. We develop a rigorous mathematical framework for quantifying metastatic phylogenetic diversity. Distant metastases are typically monophyletic and genetically similar to each other. Lymph node metastases, in contrast, display high levels of inter-lesion diversity. We validate these findings by analyzing 317 multi-region biopsies from an independent cohort of 20 patients. We further demonstrate higher levels of intra-lesion heterogeneity in lymph node than in distant metastases. Our results show that fewer primary tumor lineages seed distant metastases than lymph node metastases, indicating that the two sites are subject to different levels of selection. Thus, lymph node and distant metastases develop through fundamentally different evolutionary mechanisms.

Exhaustion of the immune system by Group A Streptococcus necrotizing fasciitis: the occurrence of late secondary infections in a retrospective study.

BACKGROUND: Necrotizing fasciitis is a potentially lethal condition for which early and adequate treatment with surgical debridement and broad-spectrum intravenous antibiotics are essential for survival. It is hypothesized that Group A Streptococcus (GAS) necrotizing fasciitis causes exhaustion of the immune system, making these patients more susceptible for late secondary infections. METHODS: A retrospective study was conducted of all patients with necrotizing fasciitis between 2002 and 2016. Patients with necrotizing fasciitis based on macroscopic findings, positive Gram staining, culture or fresh frozen section of fascia biopsies were included. Patients with necrotizing fasciitis were divided into two groups based on the presence of GAS. Of both groups, clinical course, outcome and occurrence of late secondary infections were analyzed. For the occurrence of secondary infections, pneumonia was chosen as reference for late secondary infections. RESULTS: Eighty-one patients with necrotizing fasciitis were included of which 38 (47%) had GAS necrotizing fasciitis and 43 (53%) had non-GAS necrotizing fasciitis. Patients with GAS necrotizing fasciitis were younger (50 vs. 61 years, p=0.023) and more often classified as ASA I (45% vs. 14%, p=0.002) compared with patients with non-GAS necrotizing fasciitis. In-hospital mortality rate for necrotizing fasciitis was 32%. Patients with comorbidities were more likely to die of necrotizing fasciitis compared with patients without comorbidities (OR 7.41, 95% CI 1.58 to 34.63). Twelve patients (39%) with GAS necrotizing fasciitis developed pneumonia compared with four patients (13%) with non-GAS necrotizing fasciitis (p=0.017; OR 4.42, 95% CI 1.124 to 15.79). Median time from diagnosis to development of pneumonia in patients with GAS necrotizing fasciitis was 10 days (IQR 9). CONCLUSION: Patients with GAS necrotizing fasciitis have an increased risk to develop late secondary infections during initial treatment for necrotizing fasciitis compared with patients with necrotizing fasciitis without involvement of GAS. This suggests exhaustion of the immune system after severe GAS infection. LEVEL OF EVIDENCE: III.