Baseline characteristics and propensity score matching
Between January 2010 and December 2014, 731 patients underwent IBR after mastectomy at SNUH for primary breast cancer. A total of 664 patients who meet study criteria underwent propensity score matching based on age, cancer stage18, and ER status, which resulted in the inclusion of 496 patients (247 implants and 249 flaps) for further analysis. (Supplementary fig. 1)
There were no differences between the two groups in cancer stage, chemotherapy or radiotherapy status, ER status, PR status, NG, HG, and HER2 amplification after propensity score matching (Table 1, Supplementary table 1). Of the 247 patients from implant group, 60 (24.3%) patients received implant insertion, and 187 (75.7%) received tissue expander insertion. The majority of flap reconstructions used a free transverse rectus abdominis myocutaneous (TRAM) flap (n=238, 95.6%); other used a pedicled latissimus dorsi myocoutaneous flap (n=7, 2.8%), a free superficial inferior epigastric artery perforator flap (n=1, 0.4%), a free inferior gluteal artery perforator flap (n=1, 0.4%), a free gracilis flap (n=1, 0.4%), or a free lumbar artery perforator flap (n=1, 0.4%).
Cancer recurrence after reconstruction
During median follow-up duration was 58.2 months (57.3 and 58.3 months for implant and flap group, respectively) there were 38 recurrence events. Cancer stage was an independent prognostic factor for recurrence (p<0.001). The NG (p=0.004), HG (p=0.001), and Ki-67 (p<0.001) were also prognostic factors for cancer recurrence. Vascular emboli and lymphatic emboli affected the DFI (p<0.001 and p<0.001, respectively); however, ER status (p=0.172), PR status (p=0.190), and HER-2 status (p=0.642) did not.
There was no difference in the DFI between implant group and flap group. During follow up, 14 patients relapsed in implant group and 24 patients relapsed in flap group. The 5-year DFI rate was 93% in implant group and 90% in flap group (p=0.100). (Fig. 1a) There were no differences in DFI between the patients that underwent one-stage implant and two-stage expander insertion (p=0.861) or between those that underwent TRAM flap and other types of flap reconstructions (p=0.859).
In a multivariate analysis for DFI including cancer stage, NG, HG, and Ki-67, cancer stage (p=0.007) was an independent prognostic factor (Supplementary table 2).
Systemic cancer recurrence affected by IBR method in aggressive tumors
When we considered the different cancer stages separately, there was no difference in DFI between the implant and flap group (p-value for stage 1=0.642; stage 2=0.195; stage 3=0.132). (Fig. 2)
On the other hand, when we considered the HG separately, patients with HG 3 (high HG) in flap group (n=74) had a lower 5-year DFI rate than implant group (n=75) (5-year DFI rate for implant group 92% vs. flap group 77%; p=0.012). There was no such difference among the patients with HG 1 or 2, however (p=0.917). Likewise, flap reconstruction showed short DFI in patients with high Ki-67 (p=0.028). In contrast, there was no difference in DFI between the two groups in low Ki-67 (p=0.278). When both HG and Ki-67 were considered, aggressive tumor (defined by high HG and high Ki-67) relapsed more frequently following flap reconstruction than implant reconstruction (p=0.004). (Fig. 3a-d) Patient characteristics between the two reconstruction groups in high HG and/or high Ki-67 group did not differ.
In multivariate analysis for DFI performed within high HG group considering cancer stage, hormone receptor (HR), HER2 and reconstruction type, the reconstruction type was the independent prognostic factor (p=0.018). (Table 2) Likewise, in high Ki-67 group, the reconstruction type was the independent prognostic factor for DFI in multivariate analysis (p=0.015, data not shown).
When HR and HER2 status was considered, DFI was not different between two groups in each tumor subtype: including triple-negative breast cancer (TNBC; p=0.668), and HR-positive breast cancer (p=0.230). However, in 71 aggressive tumors (high HG and high Ki-67), frequent relapse after flap reconstruction was seen especially in HR-positive breast cancers (HR-positive: p=0.008; HR-positive/HER2-negative: p=0.002), which accounts for majority of our study population. (Fig. 3e-f)
Next, we observed whether the reconstruction type affected locoregional recurrence. There were 20 locoregional recurrences during follow up: 9 in implant and 11 in flap group. The 5-year LRRFI rate was 95% in implant group and 95% in flap group (p=0.991). (Fig. 1B) Unlike the DFI, the LRRFI was not affected by reconstruction method neither in high HG tumor (p=0.445) nor in high Ki-67 tumor (p=0.791). The reconstruction type did not affect locoregional recurrence in a multivariate analysis (p=0.704).