Table 2.
Subgroup analysis for ipsilateral breast tumor recurrence (IBTR) comparing BCS + RT to BCS in DCIS women diagnosis at 50 year-old or less.
| Stratification | No. of studies | HR | 95% CI | Intra-subgroup heterogeneity (I square) | p value for inter-subgroup interaction test | |
|---|---|---|---|---|---|---|
| Cutoff age for young subgroup | <40 y/o | 6 | 0.82 | 0.48, 1.39 | 30% | 0.31 |
| 40 - 50 y/o | 8 | 0.60 | 0.43, 0.83 | 64% | ||
| Median f/u timea | <7 y | 6 | 0.45 | 0.29, 0.68 | 8% | 0.04 |
| 7–10 y | 5 | 0.82 | 0.65, 1.04 | 13% | ||
| ≥10 y | 3 | 0.80 | 0.37, 1.74 | 75% | ||
| Hormone therapy usea,b | ≥50% | 2 | 0.28 | 0.09, 0.82 | 17% | 0.17f |
| <50% | 9 | 0.62 | 0.43, 0.89 | 47% | ||
| NA | 3 | 0.92 | 0.76, 1.12 | 0% | ||
| Free surgical margina,c | ≥80% | 7 | 0.60 | 0.36, 0.99 | 61% | 0.89f |
| <80% | 6 | 0.62 | 0.46, 0.85 | 0% | ||
| NA | 1 | 0.97 | 0.78, 1.21 | – | ||
| Study design | RCT | 3 | 0.59 | 0.42, 0.83 | 0% | 0.51 |
| Obs. | 11 | 0.69 | 0.49, 0.96 | 54% | ||
| Multivariate analysisd | With | 3 | 0.67 | 0.39, 1.17 | 76% | 0.88 |
| without | 11 | 0.64 | 0.46, 0.90 | 39% | ||
| Boost irradiationa | 100% | 2 | 0.48 | 0.17, 1.34 | 0% | 0.69f |
| 1–99% | 5 | 0.62 | 0.33, 1.18 | 71% | ||
| 0% | 3 | 0.74 | 0.54, 1.02 | 0% | ||
| NA | 4 | 0.56 | 0.27, 1.16 | 66% | ||
| Patient-included yeare | before 1990 | 2 | 0.55 | 0.34, 0.89 | 0% | 0.75 |
| cross years | 6 | 0.67 | 0.41, 1.12 | 63% | ||
| after 1990 | 6 | 0.69 | 0.46, 1.03 | 48% |
BCS + RT: breast conserving surgery with adjuvant radiotherapy, BCS: breast conserving surgery, HR: hazard ratio, 95% CI: 95% confidence interval, RCT: randomized control trials, Obs.: observational studies, y/o: years old, f/u: follow-up, y: years, NA: not available.
For non-age specific studies, data of these factors from the whole study population would be taken as the proxy for the young subgroup, assuming the distributions were similar among age groups as an indicator for quality of medical care.
The incidence of positive estrogen receptor in DCIS was ranged from 49 to 77.8%[59]. Therefore, ≥ 50% was chosen as the cutoff value for subgroup analysis, indicating a more regular use of hormone therapy in the study population.
In order to compare with the EBCTCG study including 4 large RCTs having the free surgical margin rate of 80% or more, ≥ 80% was chosen as the cutoff value for subgroup analysis.
Factors corrected in studies with multivariate analysis: Omlin 2006: age, detection method, tumor size, necrosis, tumor grade, margin status, oestrogen-receptor status; Park 2018: age, year of diagnosis, race, registry region, tumor grade, histology, size, hormone receptor status; SWeDCIS: tumor size, focality, margin status, mode of detection.
Patient-included year was taken as substitutional index for technique of radiation therapy. Case inclusion before 1990 was considered at risk for suboptimal RT techniques [60].
The p value if for inter-subgroup interaction analysis test excluding the NA subgroup.