The early diagnosis and evaluation of breast cancer is of great significance to its treatment and prognosis. Among the multiple factors affecting the prognosis, the degree of axillary lymph node metastasis is one of the most vital factors.

Accurately understanding the status of axillary lymph nodes prior to surgery allows better prediction of staging, enables correct treatment plans, and guides the scope of node dissection during surgery. For patients with early breast cancer or clinically negative axillary lymph nodes, sentinel lymph node biopsy (SLNB) can largely avoid complications such as upper extremity lymphedema caused by axillary lymph node dissection (ALND). Thus, clinical identification of negative lymph nodes becomes more valuable. Based on clinical verification, the NCCN guidelines (edition 2019) made the following recommendation: SLNB is performed for patients with clinically negative axillary lymph nodes, and the biopsy findings determine whether ALND is included; ALND is performed for patients with clinically positive axillary nodes. Currently, imaging examinations have limitations is assessing axillary lymph nodes. Finding an accurate and non-invasive method in preoperative axillary assessment has been a project that needs to be urgently addressed. Ultrasonography has advantages in its simplicity, non-invasiveness, economy, and on radiation, however it is highly subjective, dependent upon examiner's experience and knowledge, and is difficult to detect deeper and small lesions. Molybdenum Target examination plays an important role in diagnosis of breast cancer, however it is expensive and limited in evaluating the whole axilla. PET-CT is restricted by its high cost and is not a routine examination in China.

Therefore, computed tomography (CT) scan is more advantageous in determination of lymph node metastasis. The 2014 GORO KUTOMI study suggested that lymph node morphology assessed as clear by preoperative CT was an independent predictor of sentinel lymph node metastasis. CT scan can not only evaluate the presence or absence of distant metastasis and pectoralis muscle invasion, but also provide intuitive, accurate and detailed evaluation of axillary, supraclavicular, and pectoralis major intramuscular lymph nodes. The diagnostic criteria of magnetic resonance imaging (MRI) is relatively vague; CT can also obtain imaging data of the lungs, mediastinum, whereas MRI has no such function. Based on previous studies, we will further explore and evaluate axillary node status using prone positioning CT scan and ultrasound in patients with breast cancer.

A total of 500 patients who are newly diagnosed with operable breast cancer in Liaoning Oncology Hospital are approached and recruited. Inclusion criteria: 1. preoperative chest CT and axillary Doppler ultrasound examination in the prone position; 2. perform ALND; 3. regular follow-up post surgery, short-term and long-term. Exclusion criteria: history of other benign or malignant tumors causing axillary lymphadenopathy.

Comparisons are made:

A: between suspiciously positive and suspiciously negative axillary lymph nodes B: between LNSD positive among suspiciously positive axillary lymph nodes and negative axillary lymph nodes f C: between positive and negative AAUS D: between positive and negative AAUS among negative lymph nodes detected by CT scan E: between positive and negative AAUS among lymph nodes with negative LNSD

Chi-square test and t test are used to assess statistical significance between groups.

Methods: Lymph node short diameter (LNSD) is measured using CT scan imaging (LNSD > 1cm is considered positive), axillary lymph node status is assessed according to axillary lymph node Doppler ultrasound. ALND will be performed in patients with positive axillary lymph nodes on CT scan; PALND will be performed for those with negative axillary lymph nodes on CT scan but positive on AAUS; SLNB will be performed for those with negative axillary lymph nodes on CT scan and on AAUS.

The prognosis in each patient group is to be evaluated by short-term observational indicators (e.g. lymphedema and/or status of axillary lymphatic return), and long-term indicators (e.g. lymphedema and/or axillary lymph node recurrence). The accuracy of CT scan assessing positive lymph nodes and positive AAUS will be evaluated according to the postoperative histology results.

Inclusion Criteria:

• Preoperative chest CT and axillary Doppler ultrasound examination in the prone position
• Perform ALND
• Regular post surgery follow-up (short-term and long-term)

Exclusion Criteria:

•History of other benign or malignant tumors causing axillary lymphadenopathy