Sample size: G\*Power software was applied for estimating the sample size. Based on the relevant study "A couple-based intervention for female breast cancer" (Baucom et al., 2009), the median interpolated effect size across all female measures at posttest was 0.61. The type I error α was set at 0.05, statistical power was set at 0.8, and the effect size was set at 0.61 by using the independent sample t-test. We estimated a total sample number of 68, comprising the sample size of 34 for the experimental group and the sample size of 34 for the control group.

Method: The women with breast cancer and their spouses as couples were randomly allocated to the treatment as usual groups or couple-based family nursing groups in a 1:1 ratio by using computer-generated randomization. All eligible participants were recruited by a research assistant from the surgical wards. Participants were randomly allocated using sequentially numbered sealed envelopes. The envelopes were opened just before the operation, the research nurse who was involved in the data collection was blinded to the group allocation, and participants were not informed of their group allocation status. All participants were given a letter that contained the details of the research and informed the patients and spouses that they had the right to abstain from the research at any time, for any reason, and that participation and lack thereof would not affect their rights to treatment and care. Each participant was informed about the research and provided their written informed consent.

Couple-based family nursing: Besides the standard care and teaching program, the nurse researcher who has well trained about the breast cancer care family nursing and couple interviewing techniques. provided the women and their spouses a 30-60 minutes couple of interviews after the standard teaching program. The detail of the couple interview was followed the core concept of the Institute for Patient and Family-Centered Care (IPFCC, 2021), dignity and respect, information sharing, participation, and collaboration. The necessary caring knowledge was provided, the important value of couple together, and caring role to help their spouses to coach and help their wives to perform the rehabilitation during the critical hospitalization stage until to discharge back to home. In this intervention stage, the research nurse empowered their spouses to assist women with daily couple-based rehabilitation with a specific workbook that contained uncomplicated illustrations demonstrating what to expect during the first 48 hours after breast surgery. Firstly, we listened to couples' perspectives and assessed couples' knowledge and skills regarding arm rehabilitation; subsequently, we could understand spouses' willingness and values regarding assistance. Secondly, we provided comprehensive and unbiased data and clarified misinformation regarding arm rehabilitation. We taught couples the following rehabilitation movements: hand squeeze, wrist, and elbow flexion and extension, pendulum exercise, finger wall-climbing exercise, hair combing, wall pushup, pulley exercise, and turning around exercise. Arm rehabilitation begins within 48 hours postoperatively, and each movement should be incrementally increased in terms of exertion and repetition until the patient reaches 10 repetitions, 2-3 times daily, for one month. Spouses were required to support patients' wrist and elbow joints and maintain the arm perpendicular to the body. Spouses were instructed that if women experience negative emotions during the rehabilitation movements, spouses can express support to his wife through body language, such as kissing, holding hands, touching, or hugging. Thirdly, we investigated the concerns related to couples' practice rehabilitation movements. We explained to couples the distinctions between rehabilitation with and without spousal assistance to encourage couples to participate in this care program. Finally, we collaborated with each couple to develop an individualized rehabilitation program.

Data analysis: All data were analyzed using SPSS software version 24.0 and following intention-to-treat principles. Descriptive statistics of demographic and clinical characteristics were evaluated using chi-square tests for categorical variables. The outcome measures were analyzed at baseline and the group × time interaction effect between the two groups at one-month post-surgery by using a generalized estimating equation. The demographic and clinical characteristics were presented as numbers and percentages (%), the outcome measures were presented as means and standard deviations for participants. The level of significance was set at p \< 0.05, and the intervention effects were considered to be significant at p ≤ 0.05.