Table 1.
Characteristics of enrolled studies.
| Study design/Enrolled studies | Countries | Enroll years | Overall population |
Young population |
|||||
|---|---|---|---|---|---|---|---|---|---|
| Case No. | Median f/u (y) | Hormone therapy use | Free margin | RT regimens | Cutoff agea | Case No. (%)b | |||
| Randomized control trialsc | |||||||||
| NSABP B-17 1998 [7] | US, Canada | 1985–1990 | 818 | 7.5 | 0% | 87% (positive or NA: 13%) | 50 Gy/25 frx; 9% with boost | 49 | 274 (33.5%) |
| EORTC 10853 2006 [6] | Europe | 1986–1996 | 1010 | 10.5 | 0% | 84% (Positive, < 1 mm, or NA: 16%) | 50 Gy/25 frx; 5% with boost | 40 | 51 (5.0%) |
| SweDCIS 2008 [18] | Sweden | 1987–1999 | 1067 | 8.4g | 0% | 80% (positive: 11%, NA: 9%) | 50 Gy/25 frx, or 48 Gy/20 frx, or 54 Gy/27 frxi; boost not recommended | 49 | 252 (23.6%) |
| Observational studies | |||||||||
| Van Zee 1999 [26] | US | 1978–1990 | 157 | 6.2 | 8% | 44% (positive: 3%, NA: 53%) | prescribed dose: 50 Gy; 100% with boost (10–20 Gy) | 39 | 15 (9.5%) |
| Cutuli 2002 [27] | France | 1985–1995 | 822 | 7.2 | NA | 78.6% (positive: 7.5%, NA: 13.9%) | minimal whole-breast dose: 45 Gy; 80% with boost (10–20 Gy) | 39 | 51 (6.2%) |
| Omlin 2006 [28] | Transnationald | 1978–2004 | 373 | 6 | 7% | 65.4% (positive: 5.4%, NA: 29.2%) | median whole breast dose: 50 Gy; 47.5% with boost (median boost dose: 10 Gy) | 45 | 373 (100%) |
| Gonzaga 2009 [29],e | Italy | 1996–2005 | 775 | 3.3 | 26.0% (ER+: 48%) | 86.3% (positive: 13.7%) | most common RT schedule: 50 Gy without boost | 40 | 72 (9.3%) |
| Tunon-de-Lara 2010 [30] | France | 1974–2003 | 207 | 13.3 | 1.0% | 85.7% in BCS (positive: 14.3%) NA in TM | 50 Gy whole breast RT; 45.5% with boost (10 Gy) | 39 | 207 (100%) |
| Alvarado 2012 [31] | US | 1996–2009 | 2037 | 5.2 | 35.7% (<40 y/o: 28.8%) | 99.8% (positive: 0.2%) | NA | 39 | 132 (6.5%) |
| Rakovitch 2013 [32] | Canada | 1994–2003 | 3762 | 10 | 17% in >65 y/o | 55.7% (positive: 13.9%, NA: 30.4%) | 50 Gy/25frx; or 40–44 Gy/16 frxj; without boost | 50 | 480 (12.8%) |
| NA in <65 y/o | |||||||||
| Worni 2015 [33] | US-SEER | 1991–2010 | 121,080 | 5.9 | NAh | NAh | NAh | 49 | 31,036 (25.6%) |
| Qian 2015 [34] | US-SEER | 1998–2007 | 56,968 | 7.6 | NAh | NAh | NAh | 50 | 15,554 (27.3%) |
| Elshof 2016 [35] | Netherland | 1989–2004 | 10,090 | 10.7 | 0% | NA | NA | 49 | 2159 (21.4%) |
| Cronin 2016 [36] | US | 1978–2010 | 2634 | 6.3 | 21% (<40 y/o: 11%) | 74% (positive: 19%, NA: 7%) < 40y/o: 71% (positive and close: 19, NA: 10%) | NA | 39 | 138 (5.2%) |
| Sagara 2016 [16] | US-SEER | 1988–2007 | 32,144 | 8 | NAh | NAh | NAh | 40 | 896 (2.8%) |
| Kim 2017 [37] | Korea | 1995–2010 | 286 | 6.4 | 61.5% | 93.7% (positive: 6.3%) | median dose: 50.4 Gy (45.0–50.4 Gy); median dose of boost: 12.6 Gy (9–20 Gy) | 50 | 286 (100%) |
| Park 2018 [17] f | US-SEER | 1998–2011 | 3648 | 7 | NAh | NAh | NAh | 40 | 3648 (100%) |
| Kuo 2018 [38] | Taiwan | 2003–2010 | 375 | 7.9 | 73.1% | 72.5% (positive and close: 27.5%) | 50 Gy/25 frx whole breast RT; 100% with boost: 10 Gy/5 frx | 39 | 45 (12%) |
| Giannakeas 2018 [39] | US-SEER | 1998–2014 | 140,366 | NA | NAh | NAh | NAh | 39 | 4657 (3.3%) |
| Van Seijen 2021 [40] | Netherland | 1989–2004 | 10,045 | 15.7 | 0% | NA | NA | 49 | 2143 (21.3%) |
| Byun 2021 [41] f | US-NCDB | 2004–2016 | 52,150 | 5.4 | 32.0% (ER+: 43.7%) | 94.5% | NA | 49 | 52,150 (100%) |
f/u: follow up, y: years, RT: radiotherapy, US: United States, SEER: Surveillance, Epidemiology, and End Results Program, NCDB: National Cancer Database, NA: not available, ER+: estrogen receptor positive, y/o: year-old, BCS: breast conserving surgery, TM: mastectomy.
The cutoff value of age as young population in each studies.
The proportion of defined young subgroup in each studies.
The UK/ANZ trial was not included due to inadequate information provided for outcome-of-interest in the young subgroup.
The cohorts included patients from Australia, Belgium, France, the UK, Israel, Italy, the Netherlands, Spain, Switzerland, Turkey, and the US.
For Gonzaga 2009, only those with grade II-III DCIS receiving breast conserving surgery were included for the meta-analysis.
For Park 2018 and Byun 2021, those receiving contralateral prophylactic mastectomy or post-mastectomy radiotherapy were not included in the meta-analysis.
The values presented were the mean values instead of median.
The prescription of tamoxifen, dose of radiotherapy, and surgical margin were not available in SEER database.
The distribution of whole breast radiation dose: 50 Gy/25 frx in 80%, 48 Gy/20 frx in 13%, 54 Gy/27 frx then 2 weeks gap in 7%.
The distribution of whole breast radiation dose: 50 Gy/25 frx in 56%, 40–44 Gy/16 frx in 36%, NA for others.