Table 1. Summary of included studies.

No.	Study	Definitions	% of EOPC patients in population	No. of EOPC patients	No. of AOPC patients	Place & period or recruitment	Median follow-up	Adjustment to survival analysis	Adjusted HR (EOPC vs. AOPC)	Median survival & survival rates (EOPC vs. AOPC)
1.	Kang JS 2017	EOPC = <45 y.o.; AOPC = 45 y.o.	4.90%	- 34 (total, before PSM) - 34 (after PSM)	- 665 (total, before PSM) - 68 (after PSM)	South Korea, 2000–2014	Not stated	No Cox regression, only PSM. PSM adjusted with patients' ASA score, AJCC stage, adjuvant chemotherapy and radiotherapy.	Not stated	- Median OS: 17 months vs. 32 months; P = 0.970 - 5-year OS: 5.4% vs. 18.0%
2.	Ansari D 2019	EOPC = <50 y.o.; LOPC = ≥ 50 y.o.	6.20%	- 3172 (after PSM)	- 3172 (after PSM)	USA, 2004–2016	Not stated	Gender, tumor size, AJCC stage 7th edition, surgery, and chemotherapy	aHR = 1.07 (95% CI 1.01–1.13; P = 0.015)	- Median survival: Not stated - 5-year OS: 6.1% vs 8.6%, p = 0.003 - 5-year CSS: 6.7% vs 9.7%, p < 0.001
3.	Saadat LV 2021	EOPC = <50 y.o.; AOPC = >= 50 y.o.	6.30%	11161 (treated pts)	92387 (treated pts)	USA, 2004–2016	30.2 months	No Cox regression, although there were subgroup analyses based on treated and untreated patients, stage 0–2 disease, stage 3–4 disease, and time period	Not stated	- Median survival: Not stated - 1-year OS for stage 0-2 disease: 72.4% (95%CI: 71.2%–73.7%) vs. 53.3% (95%CI: 52.9%–53.7%) - 1-year OS for stage 3 disease: 47.6 (95%CI: 45.1%–50.0%) vs 37.8% (95%CI: 37.1%–38.4%) - 1-year OS for stage 4 disease: 24.8% (95%CI: 23.8%–25.8%) vs 14.8% (95%CI: 14.5%–14.9%)
4.	Dai D 2019	EOPC = < 45 y.o. vs. older group	2.50%	1386	53932	USA, 2004–?	Not stated	Age, sex, race, tumor location, surgery experience, tumor size, lymph node ratio, 6 th AJCC TNM stage, grade, radiotherapy & chemotherapy experience, marital status	- aHR age < 45 y.o. vs. 45–59 y.o. = 0.93 (95% CI 0.88–0.98; P = 0.010) - aHR age < 45 y.o. vs. 60–69 y.o. = 0.91 (95% CI 0.85–0.96; P = < 0.001) - aHR age < 45 y.o. vs. 70–79 y.o. = 0.86 (95% CI 0.81–0.92; P = < 0.001) - aHR age < 45 y.o. vs. >79 y.o. = 0.85 (95% CI 0.81–0.91; P = < 0.001)	Not stated
6.	Piciucchi M 2015	EOPC = ≤ 50 y.o. at diagnosis, AOPC = age > 50 y.o. at diagnosis	8.50%	25	268	Italy, 2006–2013	Not stated	Tumor stage included, others unclear	aHR = 0.7; (95% CI 0.4–1.1; p = 0.1)	- Median OS = 11 months vs. 9 months; P = 0.28
6.	Tingstedt B 2011	EOPC = ≤ 50 y.o. at diagnosis, AOPC = age > 50 y.o. at diagnosis	5.70%	33	33	Sweden, Jan 1993–Dec 2008	Not stated	No Cox regression, but patients were matched with controls based on sex, resection, tumor size, chemotherapy and radiotherapy	Not stated	- Median OS: 5.67 months vs. 8.00 months; P = 0.12 - 5-year OS: 3.3% vs. 0%
7.	He J 2013	EOPC = ≤ 45 y.o., LOPC = ≥ 70 y.o.	7.90%	75	870	USA, 1975–2009	Not stated	No Cox regression, only subgroup analysis based on cancer stage	Not stated	- Median OS: 19 months vs. 16 months; P = 0.007 - 5-year OS = 24% vs. 11%; P = 0.005 - 10-year OS = 17% vs. 3%, P < 0.001
8.	Ordonez JE 2020	EOPC = <50 y.o.; AOPC = ≥ 50 y.o. at diagnosis	5.90%	12137	194925	USA, 2004–2013	Not stated	Age, sex, race/ethnicity, comorbidities, insurance status, tumor size, anatomic location, tumor grade/differentiation, lymph node status, AJCC stage, presence of lymphovascular invasion, and receipt of surgery, chemotherapy, or radiation	0.867 (95% CI 0.85–0.88)	- Median OS: 9.2 months vs. 6.0 months; P < 0.001
9.	Beeghly-Fadiel A 2016	EOPC = <50 y.o.; AOPC = ≥50 y.o. at diagnosis	11.50%	118	1282	USA, 1988─2013	Not stated	Age, race, year of diagnosis, AJCC stage, tumor location, treatment received, multiple malignancies, family history of pancreatic cancer	0.82 (95% CI 0.67─1.00)	- - Median OS: 9.36 months vs. 8.04 months; P = 0.403
10.	Whitley A 2023	EOPC = ≤ 50 y.o. at diagnosis, AOPC = age > 50 y.o. at diagnosis	7.00%	1324	17564	Czech Republic, 1985─2015	Not stated	No Cox regression, but had subgroup analysis based on the stage of cancer	Not stated	- Median OS: 5.9 months vs. 4.5 months; P < 0.001 - 1-year OS: 28.4% vs. 22.6%; P < 0.001 - 2-year OS: 15.3% vs. 10.1%; P < 0.001 - 3-year OS: 11.4% vs. 6.6%; P < 0.001 - 5-year OS: 8.2% vs. 4.0%; P < 0.001
11.	Castet F 2023	EOPC = ≤ 50 y.o. at diagnosis, AOPC = age ≥ 70 y.o. at diagnosis	Not stated	139	141	Spain, 2010─2022	54.8 months	Sex, history of diabetes, tobacco history, alcohol intake, clinical stage, tumor location, ECOG performance status (ECOG-PS), CA19.9 levels, albumin levels, and neutrophil-to-lymphocyte ratio (NLR)	0.87 (95% CI 0.65─1.16; P = 0.33)	- Median OS: 18.7 months vs. 17.6 months; P = 0.75
12.	Zironda A 2023	EOPC = ≤ 50 y.o. at diagnosis, AOPC = age > 50 y.o. at diagnosis	5.70%	65	1068	USA, Jan 2011─Dec 2021	22.4 months	Onset of PDAC, age, race, sex, ASA, diabetes, elevated Ca 19-9, neoadjuvant therapy, adjuvant therapy, minimally invasive surgery approach, vascular resection, major complication, IPMN pathology, tumor size, grade, lymph node involvement, R0 resection	0.93 (95% CI 0.64─1.33; P = 0.68)	- Median OS: 30.6 months vs. 31.0 months - 1-year OS: 73.3% vs. 79.5% - 3-year OS: 43.9% vs. 43.9% - 5-year OS: 33.0% vs. 31.0%
13.	Takeda T 2022	EOPC = ≤ 50 y.o. at diagnosis, AOPC = age > 50 y.o. at diagnosis	8.00%	127	1519	Japan, Jan 2010─Aug 2019	Not stated.	No Cox regression, but had subgroup analysis based on resectability of cancer	Not stated	- Median OS: 16.9 months vs. 17.1 months; P = 0.565
14.	Ren S 2023	EOPC = < 50 y.o. at diagnosis, AOPC = age ≥ 50 y.o. at diagnosis	6.90%	763	2278	USA, 2004─2018	Not stated	Sex, race, site, tumor differentiation, TNM stage and treatment patterns	Not stated	- Median OS: 9 months vs. 8 months; P = 0.002 - 1-year OS: 38.4% vs. 36.8% - 3-year OS: 11.1% vs. 10.1% - 5-year OS: 6.9% vs. 5.8%
15.	Ramai D 2021	EOPC = ≤ 40 y.o. at diagnosis, AOPC = age > 40 y.o. at diagnosis	0.87%	1181	134919	USA, 1975─2016	Not stated	Age, sex, race, tumor grade, stage, T status, N status, primary tumor site, no. of lymph node examined, no. of positive lymph nodes, receipt of surgery, chemotherapy, or radiation	0.485 (95% CI 0.422–0.557, P < 0.001)	- Median OS: 7.0 months vs. 6.0 months; P < 0.001
16.	Wang H 2020	EOPC = ≤ 40 y.o. at diagnosis, AOPC = age > 40 y.o. at diagnosis	1.12%	1422	57201	USA, 2004─2015	Not stated	Race, gender, year of diagnosis, pathological grade, AJCC stage, historic stage, tumor location	- aHR age 20–40 vs. 40–60 = 0.54 (95% CI 0.50–0.58; P < 0.001) - aHR age 20–40 vs. 60–80 = 0.45 (95% CI 0.42–0.49; P < 0.001) - aHR age 20–40 vs. >80 = 0.30 (95% CI 0.28–0.33; P < 0.001)	- Median CSS age 20–40 vs. age 40–60 vs. age 60–80 vs. age >80 = 36.0 months vs. 10.0 months vs. 8.0 months vs. 4.0 months - 5-year CSS age 20–40 vs. age 40–60 vs. age 60–80 vs. age >80: 44.7% vs. 16.9% vs. 13.8% vs. 8.7%
17.	Mendis S 2024	EOPC = ≤ 50 y.o. at diagnosis, AOPC = age > 50 y.o. at diagnosis	6.70%	112	1571	Australia, New Zealand, Singapore, Jan 2016–Dec 2021	23.6 months	No Cox regression, but has subgroup analysis based on tumor resectability	- aHR locally advanced = 0.47 (95% Cl 0.32–0.69; P = 0.005) - aHR metastatic = 0.66 (95% Cl 0.48–0.89; P =0.025)	- Median OS: 23.4 months vs 10.3 months - P < 0.001

Abbreviations: EOPC = early-onset pancreatic cancer; AOPC = average-onset pancreatic cancer; aHR = adjusted hazard ratio; AJCC = American Joint Committee on Cancer, ECOG-PS = Eastern Cooperative Oncology Group - Performance Status; OS = overall survival; PSM = propensity score matching; CSS = cancer-specific survival; IPMN = intraductal papillary mucinous neoplasms; y.o. = years old.