Here is the design of a clinical trial:

Official Title: A Multicenter, Open-label, Single-arm, Phase II Clinical Trial of Nab-paclitaxel in Combination With Pyrotinib in Adjuvant Therapy for Lymph Node-negative and Small Tumor HER2-positive Breast Cancer

Included conditions:
- Early Breast Cancer

Study Armgroups:
- {'label': 'Nab-paclitaxel in combination with pyrotinib treatment group', 'type': 'EXPERIMENTAL', 'description': 'Nab-paclitaxel 260mg/m2 every 3 weeks for 12 weeks plus pyrotinib 240mg daily for one year', 'interventionNames': ['Drug: Nab-paclitaxel in combination with pyrotinib']}

Interventions:
- {'type': 'DRUG', 'name': 'Nab-paclitaxel in combination with pyrotinib', 'description': 'Nab-paclitaxel I.V. 260mg/m2 every 3 weeks for 12 weeks plus pyrotinib oral 240mg daily for one year', 'armGroupLabels': ['Nab-paclitaxel in combination with pyrotinib treatment group']}

Primary Outcomes:
- {'measure': '3-year-DFS', 'description': '3-years-disease free survival rate', 'timeFrame': 'From the start of treatment to 3 years'}

Please estimate the sample size based on the assumption: 
One-sided significance level of 5%, power of 80%, and a dropout rate of 10%.
Sample size calculation
        The group-sequential Poisson test based on the number of events of invasive disease or any-cause death was used for sample size calculation. In designing the trial, a 3-year event rate ofââ¥â12.4% was considered to be unacceptable in this population, andââ¤â7.2% would be considered as a success [20, 21]. Assuming that the one-sided significance level is 5% and the power is 80%, the sample size should be 253. Considering a dropout rate of 10%, the target number of patients was determined as 261.