As outlined in the brief summary, three sub-studies will be embedded within the main study sample. The following section provides a concise overview of the methodological approach for each of these sub-studies.
- The longitudinal effect of decongestive lymphatic therapy:
This sub-study examines the (long-term) effect of DLT on symptoms and functioning in women with persistent breast and/or truncal oedema following breast cancer treatment. The analysis will focus on participants in the control group, who receive DLT alone. Outcomes such as symptom burden (BrEQ), local tissue water (PWC), pain (VAS), and quality of life (EQ-5D-5L and EORTC-QLQ-BR23) will be tracked at multiple time points: baseline, after 1 month of intervention, and 3 and 6 months after the end of the intervention.
No additional intervention is introduced beyond the standard treatment already described in the main study protocol. The sub-study will assess the sustainability of symptom improvement over time and provide insight into the standalone effectiveness of DLT.
- Responsiveness of the Breast Edema Questionnaire:
This sub-study aims to evaluate the responsiveness of the BrEQ, a validated questionnaire used to assess symptoms related to breast oedema. Although the BrEQ has demonstrated strong psychometric properties, its ability to detect clinically meaningful changes over time has not yet been investigated.
Participants from both groups in the main study can participate in this sub-study. The design follows a longitudinal cohort structure integrated into the RCT, without any additional interventions. Two subgroups will be analysed: (1) the intensive phase group (from baseline to one month after the start of the intervention), in which clinical improvement is expected, and (2) the maintenance phase group (from three to four months after the end of the intervention), in which symptom levels are expected to remain stable.
In both groups, BrEQ scores will be compared with patient-reported change using the Global Perceived Effect (GPE) scale. Responsiveness will be quantified through Receiver Operating Characteristic (ROC) curve analysis, and effect size calculations (Cohen's d, standardized response mean). This sub-study requires no additional interventions and uses existing follow-up time points supplemented by one extra BrEQ and GPE assessment at four months after the end of the intervention.
- Pressure and comfort of compression bras:
This sub-study investigates the pressure exerted by different commercially available compression bras and evaluates patient-reported comfort. The goal is to assess whether these garments provide adequate therapeutic compression and are acceptable for daily use.
The design follows a cross-sectional approach conducted in a subset of participants (five participants per cup size) who consent to this additional component. Each participating patient will receive different compression bras, worn for one week each.
Pressure beneath the garment will be measured using the PicoPress device (Microlab, Italy) on the first day of wear. After each one-week wear period, participants will complete an adapted version of the ICC Compression Questionnaire (ICC-CQ) to assess comfort and usability.
