Nieke Smeins, Maastricht Universitair Medisch Centrum +

Purpose:
This study investigates the frequency, extent and location of residual fibroglandular tissue (RFGT) according to breast MRI after mastectomy and DIEP flap reconstruction. Possible risk factors for RFGT and the effect of RFGT on local breast cancer recurrence risk is also investigated.

Methods:
This retrospective, single-centre study included female patients after therapeutic or prophylactic mastectomy followed by DIEP-flap reconstruction. All included women underwent postoperative breast MRI during follow-up between 2007-2022. Breast MRI exams were reassessed on presence, diameter and location of RFGT. Additional clinical data per patient was collected. Relative risk was calculated to identify possible risk factors for RFGT. To determine the association with local disease recurrence a survival analysis was performed.

Results:
A total of 73 patients were included (mean age 45 years, range 21-68). 66 out of 73 patients were diagnosed with breast cancer. RFGT was detected in 20 (27.4%) patients, with a mean diameter of 13.5 mm (range 6-31), most frequently located in the upper outer quadrant of the breast (40% of RFGT areas). Tumour grade 3 was the only statistically significant identified risk factor for presence of RFGT (RR= 2.7, CI 95%= 1.1-6.6, p= 0.024). Within a median follow-up time of 110.0 months (range 14-354), in 13 patients a local recurrence had occurred. The risk of local recurrence was higher in patients with RFGT after adjustment for important risk factors for local recurrence with a hazard ratio of 2.5, although not statistically significant (95% CI: 0.603-10.422, p=0.206).

Conclusion:
RFGT is frequently detected on breast MRI after mastectomy and DIEP flap breast reconstruction and it might be associated with local recurrence. A single breast MRI exam in follow-up after this surgical treatment could be considered relevant to detect RFGT.