Fine Needle Aspiration Cytology (FNAC)—also called fine needle aspiration—is a minimally invasive diagnostic test used to collect a small cellular sample from a lump, swelling, or mass. A clinician inserts a very thin needle (similar to a blood-draw needle) into the area of concern—commonly the thyroid (thyroid nodule), breast (breast lump), or a lymph node—and withdraws a small amount of cells. The sample is placed on glass slides and examined under a microscope by a pathology specialist. This microscopic examination is called cytology.

FNAC does not “measure” a number like a blood test. Instead, it evaluates the appearance and pattern of cells to help determine whether a lump is likely benign (non-cancerous), malignant (cancerous), infectious, inflammatory, or otherwise abnormal. In many cases, FNAC helps guide next steps—such as reassurance and monitoring, additional imaging, a core biopsy, surgery, or treatment for infection.

Results are typically reported in descriptive pathology terms and may be grouped into categories such as:

• Benign / non-cancerous: Cells look consistent with non-cancer causes (for example, a cyst, benign thyroid nodule, or reactive lymph node). This often supports observation or routine follow-up, depending on symptoms and imaging.
• Malignant / suspicious for malignancy: Cells show changes concerning for cancer. This usually triggers referral for definitive diagnosis and management (often additional biopsy or surgery and staging tests).
• Atypical / indeterminate: Some cellular changes are present but are not clearly benign or malignant. Further testing may be recommended (repeat FNAC, ultrasound guidance, molecular testing in thyroid nodules, or a different type of biopsy).
• Non-diagnostic / insufficient sample: Not enough cells were obtained to interpret reliably. This can happen especially with cystic or very small lesions and often leads to a repeat, frequently with ultrasound guidance.

FNAC is often performed in an outpatient setting. It usually takes only a few minutes, may cause brief discomfort, and typically has a low risk of complications (most commonly mild soreness or a small bruise).

Doctors order FNAC when there is a lump or abnormal swelling that needs clarification—especially when imaging (such as ultrasound or mammography) suggests a sample should be checked to rule out cancer or identify a treatable cause. FNAC is widely used because it can provide fast, useful information without a surgical incision.

Common reasons for FNAC include:

• Thyroid nodule evaluation (thyroid test): A new or growing thyroid lump, abnormal thyroid ultrasound features, or a nodule above a certain size may prompt FNAC to check for thyroid cancer or benign thyroid disease.
• Breast lump assessment (breast biopsy option): A palpable breast lump or a suspicious area on imaging may be sampled to distinguish a benign cyst/fibroadenoma from cancer. (Some cases may require core needle biopsy instead, depending on imaging and clinical factors.)
• Lymph node evaluation: Enlarged lymph nodes (neck, armpit, groin) that persist, grow, or look suspicious may be sampled to assess for lymphoma, metastatic cancer, or infections like tuberculosis.
• Salivary gland or neck masses: Lumps in the parotid/submandibular glands or other neck masses may be evaluated to determine whether they are benign tumors, cancers, or inflammatory conditions.
• Skin or soft tissue lumps: Subcutaneous nodules, cysts, or soft tissue masses may be tested when the cause is unclear.
• Unexplained swelling or symptoms: A persistent lump associated with pain, rapid growth, hoarseness (with thyroid/neck masses), difficulty swallowing, unexplained weight loss, night sweats, or fever may prompt sampling as part of a broader workup.

FNAC is especially helpful for cancer diagnosis and triage: it can quickly identify many benign conditions (reducing unnecessary surgery) and can also detect malignant cells early so treatment planning can begin sooner.

• Benign thyroid nodules and multinodular goiter
• Thyroid cancer (e.g., papillary thyroid carcinoma)
• Breast cysts and benign breast disease (e.g., fibroadenoma)
• Breast cancer (including suspected malignant breast lumps)
• Reactive (benign) lymph node enlargement due to infection or inflammation
• Lymphoma (when suspected; may require additional tests for full classification)
• Metastatic cancer to lymph nodes (spread from cancers such as head and neck, breast, lung, or melanoma)
• Tuberculous lymphadenitis and other granulomatous infections
• Salivary gland tumors (benign and malignant)
• Abscesses and localized bacterial infections (when pus or inflammatory cells are found)

• Early detection and confirmation of suspected cancer (supporting timely treatment decisions)
• Clarifying whether a lump is benign vs. malignant to reduce unnecessary surgery
• Thyroid nodule screening and risk assessment (thyroid ultrasound follow-up decisions)
• Breast health evaluation when a new lump is found (guiding next diagnostic steps)
• Investigating persistent enlarged lymph nodes to identify infection, inflammation, or cancer spread
• Guiding personalized care planning (deciding between monitoring, repeat testing, biopsy, or surgery)
• Providing reassurance when results support a benign diagnosis, paired with appropriate follow-up