core needle biopsy

**Definition & technique** - A hollow, spring-loaded cutting needle (often 14-gauge for breast) is passed through a small skin incision under local anesthesia, usually with image guidance. It obtains multiple tissue "cores" (about 1–2 cm long) that keep tissue architecture intact. - Vacuum-assisted devices can sample more tissue. A marker clip is usually placed in the lesion so it can be found again for later excision or neoadjuvant therapy.

**Comparison with other biopsy methods (high-yield)** - **Fine-needle aspiration (FNA):** 20–25 gauge needle. It yields cells for cytology only, with no architecture. It cannot distinguish invasive carcinoma from DCIS. Insufficient samples are common. It is best for thyroid nodules, cystic lesions, and lymph node sampling. It is also used for a simple breast cyst, where it is both diagnostic and therapeutic. - **Core needle biopsy:** Gives histology with architecture. It can distinguish invasive from in situ disease. It allows immunohistochemistry (ER, PR, HER2, Ki-67). It has a lower false-negative rate than FNA. - **Excisional biopsy:** Removes the entire lesion. It is used when CNB is nondiagnostic or discordant, or for certain high-risk lesions such as atypical hyperplasia on core or a radial scar. - **Incisional biopsy:** Removes part of a large lesion. It is used for suspected soft-tissue sarcoma. Plan the incision so the tract can be excised later.

**Clinical uses** - **Breast:** The standard for a palpable mass or BI-RADS 4–5 imaging lesion. Management follows the sequence: clinical exam → imaging (US if under age 30; mammogram plus US if age 30 or older) → CNB. - **Other organs:** Liver (parenchymal disease, mass), kidney (renal disease), prostate (12-core transrectal or transperineal biopsy after elevated PSA or abnormal DRE or MRI), lymph nodes (lymphoma requires architecture, so core or excisional biopsy is preferred over FNA), and bone or soft-tissue masses. - **Lymphoma:** FNA is inadequate because nodal architecture is needed. Excisional node biopsy is the gold standard, and CNB is an alternative if excision is not feasible.

**Advantages** - Minimally invasive, outpatient, and low cost. - Allows definitive diagnosis and treatment planning before surgery, which can avoid unnecessary operations or allow a single definitive surgery.

**Complications** - Bleeding or hematoma (the main risk with liver, kidney, and prostate biopsy, so check coagulation status and platelets). - Infection, pain, and pneumothorax (lung or chest wall). - Rare tumor seeding along the needle tract. - Sampling error. If histology is discordant with imaging or clinical suspicion, repeat the biopsy or proceed to excision.

**Pearls for boards** - Excisional biopsy first is not the answer for a new breast mass. Do CNB (image-guided if needed) first. - A bloody aspirate or a residual mass after cyst aspiration needs further workup (CNB or excision). - Atypical ductal hyperplasia or lobular neoplasia on core biopsy has a risk of upstaging, so surgical excision is generally recommended. - Core biopsy is preferred over FNA when architecture matters: lymphoma, invasive vs in situ breast cancer, and organ parenchymal disease.