Purpose: The classification of the International Germ-Cell Cancer Collaborative Group (IGCCCG) has been a major advance in the management of germ-cell tumors, but relies on data of only 660 patients with seminoma treated between 1975 and 1990. We re-evaluated this classification in a database from a large international consortium., Materials and Methods: Data on 2,451 men with metastatic seminoma treated with cisplatin- and etoposide-based first-line chemotherapy between 1990 and 2013 were collected from 30 institutions or collaborative groups in Australia, Europe, and North America. Clinical trial and registry data were included. Primary end points were progression-free survival (PFS) and overall survival (OS) calculated from day 1 of treatment. Variables at initial presentation were evaluated for their prognostic impact. Results were validated in an independent validation set of 764 additional patients., Results: Compared with the initial IGCCCG classification, in our modern series, 5-year PFS improved from 82% to 89% (95% CI, 87 to 90) and 5-year OS from 86% to 95% (95% CI, 94 to 96) in good prognosis, and from 67% to 79% (95% CI, 70 to 85) and 72% to 88% (95% CI, 80 to 93) in intermediate prognosis patients. Lactate dehydrogenase (LDH) proved to be an additional adverse prognostic factor. Good prognosis patients with LDH above 2.5× upper limit of normal had a 3-year PFS of 80% (95% CI, 75 to 84) and a 3-year OS of 92% (95% CI, 88 to 95) versus 92% (95% CI, 90 to 94) and 97% (95% CI, 96 to 98) in the group with lower LDH., Conclusion: PFS and OS in metastatic seminoma significantly improved in our modern series compared with the original data. The original IGCCCG classification retains its relevance, but can be further refined by adding LDH at a cutoff of 2.5× upper limit of normal as an additional adverse prognostic factor., Competing Interests: Jörg BeyerHonoraria: Roche, Janssen Oncology, AstraZeneca, Astellas Pharma, Bayer, Ipsen Gedske DaugaardConsulting or Advisory Role: Sanofi/Aventis, Astellas Pharma, Bayer, MSD Oncology, Bristol-Myers Squibb/PfizerTravel, Accommodations, Expenses: Astellas Pharma Darren R. FeldmanResearch Funding: Novartis, Seattle Genetics, Decibel Therapeutics, Astellas PharmaOther Relationship: UpToDate Alexey TryakinConsulting or Advisory Role: BioCad, Roche/Genentech, Bristol-Myers Squibb, Eisai, Merck Sharp & DohmeSpeakers' Bureau: Bayer Health, BioCad, Lilly, Merck Serono, Sanofi, Amgen, Bristol-Myers Squibb, Eisai, Merck Sharp & DohmeTravel, Accommodations, Expenses: Novartis, BioCad, Bayer, Veropharm, Sanofi Olof StahlHonoraria: Bayer Enrique Gonzalez-BillalabeitiaTravel, Accommodations, Expenses: Bristol-Myers Squibb, Pfizer, Janssen-Cilag, Astellas Pharma, Sanofi, Roche Ugo De GiorgiConsulting or Advisory Role: Pfizer, Janssen, Astellas Pharma, Sanofi, Bristol-Myers Squibb, Bayer, Ipsen, Merck, MSD, PharmaMar, NovartisResearch Funding: Sanofi, AstraZeneca, RocheTravel, Accommodations, Expenses: Bristol-Myers Squibb, Ipsen, Janssen, Pfizer, Roche Stephane CulineConsulting or Advisory Role: Bayer, Janssen, Astellas PharmaSpeakers' Bureau: Takeda, JanssenResearch Funding: Astellas PharmaTravel, Accommodations, Expenses: Ipsen, Janssen Ronald De WitHonoraria: Sanofi, Merck Sharp & DohmeConsulting or Advisory Role: Sanofi, Merck Sharp & Dohme, Janssen, Bayer, Astellas PharmaResearch Funding: Sanofi, BayerTravel, Accommodations, Expenses: Bayer Aaron HansenConsulting or Advisory Role: Merck, GlaxoSmithKline, Bristol-Myers Squibb, EisaiResearch Funding: Karyopharm Therapeutics, Merck, Bristol-Myers Squibb, Boehringer Ingelheim, GlaxoSmithKline, Roche/Genentech, Janssen, AstraZeneca/MedImmune, Astellas Pharma, Macrogenics Marko BebekHonoraria: Roche, Novartis, Janssen Oncology, Sanofi, Sandoz, Astellas PharmaResearch Funding: Roche, Astellas PharmaTravel, Accommodations, Expenses: Roche, Astellas Pharma, Sanofi, Janssen, Novartis Angelika TerbuchResearch Funding: Roche, AstraZeneca, MSD, Bristol-Myers Squibb Costantine AlbanyStock and Other Ownership Interests: AdvaxisHonoraria: Sanofi, AstraZeneca, Seattle GeneticsConsulting or Advisory Role: Seattle Genetics, AstraZeneca/MedImmuneSpeakers' Bureau: SanofiResearch Funding: Astex Pharmaceuticals, Merck, Bristol-Myers Squibb, Lilly, BayerTravel, Accommodations, Expenses: Sanofi Marcus HentrichConsulting or Advisory Role: Amgen, Janssen-Cilag, Sanofi, Hexal, Jazz Pharmaceuticals, TakedaSpeakers' Bureau: Amgen, Janssen-Cilag, Sanofi, Takeda, Bristol-Myers Squibb, Gilead SciencesTravel, Accommodations, Expenses: Celgene, Janssen-Cilag, Takeda Jourik A. GietemaResearch Funding: Roche/Genentech, Abbvie, Siemens Robert A. HuddartEmployment: Aspen Parkside HospitalLeadership: Cancer Clinic London limited liability partnershipHonoraria: Janssen OncologyConsulting or Advisory Role: Bristol-Myers Squibb, Roche, Merck Sharp & Dohme, Janssen Oncology, Nektar, BayerSpeakers' Bureau: Roche, MSDResearch Funding: Merck Sharp & Dohme, Roche, Bristol-Myers Squibb, JanssenPatents, Royalties, Other Intellectual Property: Royalties for drug discovery from JanssenTravel, Accommodations, Expenses: Janssen Oncology, Roche/Genentech, MSD Oncology, Nektar Anja LorchHonoraria: MSD Oncology, Merck, MSDConsulting or Advisory Role: Bristol-Myers Squibb, Novartis, AstraZeneca, Roche, MSD Oncology, Janssen Oncology, Ipsen, Merck, PfizerTravel, Accommodations, Expenses: Ipsen, AstraZeneca Daniel Y. C. HengConsulting or Advisory Role: Pfizer, Novartis, Bristol-Myers Squibb, Janssen, Astellas Pharma, Ipsen, Eisai, MerckResearch Funding: Pfizer, Novartis, Exelixis, Bristol-Myers Squibb, Ipsen Christopher J. SweeneyStock and Other Ownership Interests: LeuchemixConsulting or Advisory Role: Sanofi, Janssen Biotech, Astellas Pharma, Bayer, Genentech/Roche, AstraZeneca, Pfizer, Amgen, Celgene, LillyResearch Funding: Janssen Biotech, Astellas Pharma, Sanofi, Bayer, Dendreon, PfizerPatents, Royalties, Other Intellectual Property: Leuchemix, Parthenolide, Dimethylaminoparthenolide. Exelixis: Abiraterone plus cabozantinib combination Eric WinquistHonoraria: Merck, Bayer, Eisai, Amgen, RocheResearch Funding: Roche/Genentech, Merck, Pfizer, Eisai, Ayala Pharmaceuticals Peter GrimisonResearch Funding: Tilray, Pfizer, MSD, Gilead Sciences, Boston Biomedical, Tigermed, Halozyme, Specialised Therapeutics, Medimmune, Pfizer, ASLAN Pharmaceuticals, Genentech, Eisai, Five Prime Therapeutics, QED Therapeutics, Janssen-Cilag Andrea NecchiEmployment: BayerStock and Other Ownership Interests: BayerHonoraria: Roche, Merck, AstraZeneca, Janssen, Foundation Medicine, Bristol-Myers SquibbConsulting or Advisory Role: Merck Sharp & Dohme, Roche, Bayer, AstraZeneca, Clovis Oncology, Janssen, Incyte, Seattle Genetics/Astellas, Bristol-Myers Squibb, Rainier Therapeutics, GlaxoSmithKline, FerringResearch Funding: Merck Sharp & Dohme, AstraZeneca, IpsenTravel, Accommodations, Expenses: Roche, Merck Sharp & Dohme, AstraZeneca, Janssen, Rainier TherapeuticsOther Relationship: Bayer Ben TranHonoraria: Astellas Pharma, Janssen-Cilag, Sanofi, Tolmar, Amgen, Bristol-Myers SquibbConsulting or Advisory Role: Amgen, Astellas Pharma, Bayer, Sanofi, Tolmar, Janssen-Cilag, Bristol-Myers Squibb, Ipsen, MSD Oncology, IQvia, Novartis, Pfizer/EMD Serono, AstraZeneca, Roche Molecular DiagnosticsResearch Funding: Astellas Pharma, Janssen-Cilag, Amgen, Pfizer, Genentech, AstraZeneca, Bayer, Bristol-Myers Squibb, Merck Sharp & Dohme, IpsenTravel, Accommodations, Expenses: Amgen, Astellas Pharma Axel HeidenreichHonoraria: Amgen, Astellas Pharma, Bayer, Ferring, Ipsen, Janssen-Cilag, Sanofi, TakedaConsulting or Advisory Role: Astellas Pharma, Bayer, Janssen-Cilag, Clovis Oncology, BMS Global, AstraZeneca, MSD OncologySpeakers' Bureau: Amgen, Astellas Pharma, Bayer, Ipsen, Johnson & Johnson, Sanofi, Takeda, PfizerResearch Funding: Astellas Pharma, Bayer, Sanofi, Bristol-Myers Squibb Jonathan ShamashSpeakers' Bureau: Pfizer/EMD Serono Cora N. SternbergConsulting or Advisory Role: Bayer, MSD, Pfizer, Roche, Incyte, AstraZeneca, Merck, Medscape, UroToday, Astellas Pharma, Genzyme, Immunomedics, Foundation Medicine David J. VaughnResearch Funding: Merck Sharp & Dohme, Roche/Genentech, Astellas Pharma Ignacio DuranHonoraria: Bristol-Myers Squibb, Ipsen, Roche/Genentech, Janssen Oncology, MSD Oncology, Astellas Pharma, EUSA PharmaConsulting or Advisory Role: Roche/Genentech, MSD Oncology, Bayer, Bristol-Myers Squibb, Seattle Genetics, Pharmacyclics, Janssen Oncology, Novartis, ImmunomedicsResearch Funding: Roche/Genentech, AstraZeneca Spain, Janssen Oncology, Astellas PharmaTravel, Accommodations, Expenses: Roche/Genentech, AstraZeneca Spain, Ipsen Carsten BokemeyerHonoraria: Merck KGaA, Sanofi, Roche, Bayer, Bristol-Myers Squibb, AstraZeneca, Merck Sharp & DohmeConsulting or Advisory Role: Lilly/ImClone, Merck Serono, Sanofi, Bayer Schering Pharma, Merck Sharp & Dohme, GSO, AOK Health InsuranceResearch Funding: Abbvie, ADC Therapeutics, Agile Therapeutics, Alexion Pharmaceuticals, Amgen, Apellis Pharmaceuticals, Astellas Pharma, AstraZeneca, Bayer, BerGenBio, Blueprint Medicines, Bristol-Myers Squibb, Boehringer Ingelheim, Celgene, Daiichi Sankyo, Eisai, Gilead Sciences, Glycotope GmbH, GlaxoSmithKline, Incyte, iOMEDICO, Isofol Medical, Janssen-Cilag, Karyopharm Therapeutics, Lilly, Millennium, MSD, Nektar, Novartis, Rafael Pharmaceuticals, Roche, Springworks Therapeutics, Taiho PharmaceuticalTravel, Accommodations, Expenses: Merck Serono, Sanofi, Pfizer, Bristol-Myers Squibb Anna PatrikidouConsulting or Advisory Role: Basilea Richard CathomasHonoraria: Janssen-Cilag, Astellas Pharma, Bristol-Myers Squibb, Debiopharm GroupConsulting or Advisory Role: Astellas Pharma, Bristol-Myers Squibb, Pfizer, Roche, MSD Oncology, Janssen-Cilag, Bayer, Sanofi, IpsenTravel, Accommodations, Expenses: AstraZeneca Silke GillessenConsulting or Advisory Role: Astellas Pharma, Janssen, Bayer, Orion Pharma GmbH, Tolero Pharmaceuticals, MSD Oncology, Roche, Amgen, PfizerSpeakers' Bureau: Janssen-CilagPatents, Royalties, Other Intellectual Property: Method for biomarker (WO 3752009138392 A1)Travel, Accommodations, Expenses: ProteoMedixOther Relationship: ProteoMediX, Aranda PharmaNo other potential conflicts of interest were reported.