Key words: Breast fine-needle aspiration, FNA, Clinical decision-making, Pre-treatment assessment, Multidisciplinary diagnosis and treatment

The value of breast fine-needle aspiration is far beyond the simple binary judgment of "benign or malignant." In the modern multidisciplinary diagnosis and treatment model for breast cancer, the cytological information provided by FNA is profoundly influencing the entire process from preoperative assessment, treatment plan selection to efficacy monitoring from multiple dimensions.

Preoperative Assessment and Surgical Planning

For patients with confirmed or highly suspected malignancy, FNA (fine needle aspiration) is an important tool for preoperative assessment.

• Assessment of axillary lymph node status: This is one of the most influential applications of FNA (Fine Needle Aspiration). Before radical mastectomy for breast cancer, FNA is performed on suspicious axillary lymph nodes under ultrasound guidance. If the cytology is positive, the axillary lymph node dissection can be directly planned, avoiding the unnecessary "sentinel lymph node biopsy" step. This not only saves surgical time but also secures a more timely systemic treatment window for the patient. Studies have shown that the specificity of FNA for axillary lymph node metastasis is close to 100%, and its positive predictive value is extremely high.
• Differentiation of multiple lesions: When there are two or more discrete suspicious lesions within the breast, FNA can sample different locations of the lesions separately. If the cytology shows that one lesion is invasive cancer and the other is atypical hyperplasia or carcinoma in situ, this will directly determine whether the surgical scope is total mastectomy or breast-conserving surgery combined with local expansion resection of multiple quadrants.

Guide the Implementation of Neoadjuvant Therapy

Neoadjuvant chemotherapy has become the standard treatment modality for locally advanced breast cancer. FNA plays a dual role in this process:

1. Baseline confirmation before treatment: Before initiating neoadjuvant therapy, a clear pathological diagnosis must be established. Although core needle biopsy can provide more histological information, in certain cases (such as when the tumor is extremely superficial and the patient has mild coagulation dysfunction), FNA becomes the preferred method due to its minimal trauma and lowest risk of bleeding. A high-quality FNA report, if it can clearly identify cancer cells, is sufficient to serve as the basis for initiating neoadjuvant chemotherapy.
2. Preliminary screening of molecular markers: Although the number of cells obtained by FNA is limited, modern immunocytochemical techniques can now detect the expression of estrogen receptors, progesterone receptors, and HER2 on cell smears. Although the accuracy is slightly lower than that of tissue block testing, for patients who cannot tolerate core needle biopsy, the molecular information provided by FNA can provide important clues for the initial selection of endocrine therapy or targeted therapy.

Monitoring of Therapeutic Efficacy During the Treatment Process

During the neoadjuvant treatment period, doctors need to dynamically assess the response of the tumor. At this time, FNA once again demonstrates its unique advantages.

• Early efficacy assessment: After completing 1-2 cycles of neoadjuvant chemotherapy, perform FNA on the primary tumor. If the cells drawn are largely necrotic or degenerated, it indicates effective treatment; conversely, if a large number of active tumor cells can still be easily obtained, it may suggest resistance and the need to consider changing the treatment plan. This "real-time" biological feedback is difficult to be fully replaced by imaging examinations.
• Qualitative determination of residual lesions: After neoadjuvant treatment, if the imaging shows significant reduction or disappearance of the tumor, it is still necessary to confirm whether there are microscopic residuals. At this time, performing precise FNA in the original tumor bed area can determine whether there are surviving tumor cells, providing a basis for whether supplementary radiotherapy or adjustment of endocrine therapy is needed in the future.

Application in Research and Clinical Trials

In translational medical research, FNA (Fine Needle Aspiration) is a valuable minimally invasive sampling tool. Researchers can obtain tumor cells from the same patient multiple times before and after treatment through FNA, which is used to study the molecular mechanisms of drug action, search for biomarkers for predicting therapeutic efficacy, and explore drug resistance pathways. This "cell biopsy," in addition to "liquid biopsy," provides a unique tissue source for precision medicine research.

In conclusion, breast fine-needle aspiration has evolved from a simple diagnostic tool to a multi-functional platform that runs through the entire cycle of breast cancer diagnosis and treatment. Every application of it in clinical decision-making reflects the core values of modern medicine, which are "more precise, more minimally invasive, and more individualized." of breast cancer to a higher level.