Can Bethesda III or IV Thyroid Nodules Avoid Surgery?

Getting a biopsy result back with the words Bethesda III or Bethesda IV can be incredibly stressful, but it does not automatically mean you have cancer or that you immediately need surgery. These categories are considered “indeterminate.” This means that under the microscope, the cells from your thyroid nodule look slightly unusual, but they do not have the clear, definitive features of malignancy (cancer). Because the fine-needle aspiration (FNA) biopsy cannot give a strict “yes” or “no,” your care team will look at other factors—like the nodule’s appearance on an ultrasound and advanced testing—to figure out the safest next step for your specific situation.

Because you have a multinodular goiter, it is important to remember that each nodule is assessed independently. Having nodules on both sides of your thyroid does not automatically mean your entire thyroid must be removed ^[1][2]. Your doctor will also check your blood levels (like TSH) to see if any nodules are overproducing thyroid hormone, which can change how your goiter is managed.

Understanding Bethesda III and IV Risk Levels

When a pathologist looks at an FNA biopsy, they use the Bethesda System to grade the cells.

• Bethesda III (also called AUS or FLUS) stands for “Atypia of Undetermined Significance” or “Follicular Lesion of Undetermined Significance.” The cells show some mild changes, but not enough to be called clearly suspicious ^[3].
• Bethesda IV (also called FN or SFN) stands for “Follicular Neoplasm” or “Suspicious for a Follicular Neoplasm.” The cells are crowded together in a specific pattern that requires a closer look ^[4].

The actual risk of cancer for these nodules is lower than historically thought. In one major summary, the estimated malignancy risk for Bethesda III was around 10% to 30% ^[5]. Furthermore, modern estimates are heavily influenced by the reclassification of a very low-risk, indolent (slow-growing) tumor known as NIFTP (Non-Invasive Follicular Thyroid Neoplasm with Papillary-like Nuclear Features). When NIFTP is excluded from cancer statistics, the observed malignancy risks drop even further. For example, in one surgical study, excluding NIFTP lowered the cancer risk of Bethesda III nodules from 42.3% to 22.3%, and Bethesda IV nodules from 48.7% to 17.9% ^[6][7].

Keep in mind that these are general estimates. Your personal risk heavily depends on how suspicious the nodule looks on an ultrasound—such as having irregular borders or tiny calcium deposits (often graded using a system like ACR TI-RADS) ^[8][9].

Options After an Indeterminate Result

Before deciding on surgery, your team can review several options to help clarify the risk and determine if the nodule can be safely monitored:

• Repeat Biopsy (FNA): Especially for Bethesda III, repeating the biopsy after a period of time is one option. In some cases, a repeat biopsy returns a clear, benign (non-cancerous) result ^[10]. However, this is not a guarantee; the nodule may remain indeterminate, and the choice to repeat the FNA depends on your ultrasound features and clinical symptoms ^[11].
• Molecular Testing: The sample from your biopsy can be sent for advanced molecular testing (such as Afirma GSC or ThyroSeq v3). This looks for specific genetic mutations in the nodule’s DNA and RNA—it is not a test of your family’s inherited genetics. If the test comes back negative, it significantly lowers the risk of cancer ^[12]. In some studies, a negative result has a 95% to 99% negative predictive value ^[13][14]. However, this residual risk depends on the specific assay used, your baseline ultrasound risk, and local cancer rates. A negative test lowers risk but does not make cancer impossible.
• Active Surveillance: If a repeat biopsy is benign, your molecular test is negative, or your ultrasound shows a low-risk pattern, your doctor may consider active surveillance ^[15]. This requires a reliable plan of regular follow-up ultrasounds to monitor the nodule for growth or changes, rather than removing it ^[13][8].

Note: Always contact your care team promptly if you experience rapidly worsening neck swelling, new or worsening trouble breathing or swallowing, or significant new hoarseness.

The “Follicular” Dilemma: Why Biopsies Have Limits

If your nodule is Bethesda IV, you might wonder why the pathologist can’t just look closer at the cells to see if it is a follicular thyroid carcinoma (cancer) or a follicular adenoma (a benign lump).

The reason is a fundamental limitation of cell biopsies. Under a microscope, the individual cells of a benign follicular adenoma can look very similar on an FNA biopsy to the cells of a follicular carcinoma ^[16][17]. Definitive classification usually requires seeing how the cells behave at the borders of the nodule. Pathologists must examine the entire capsule (the outer fibrous shell of the nodule) to see if the tumor cells are invading through the capsule or growing into nearby blood vessels ^[18][17]. Because a needle biopsy only extracts loose cells from the center of the nodule, it cannot capture the intact capsule. Therefore, a definitive diagnosis requires surgical removal of the nodule so the entire border can be evaluated ^[16].

If Surgery is Considered: Lobectomy vs. Total Thyroidectomy

If testing suggests a higher risk, or if your symptoms make surgery the safest option, having an indeterminate biopsy does not mandate that your entire thyroid be removed.

• Diagnostic Lobectomy: For a single indeterminate nodule that requires surgery, removing just the half of the thyroid containing the nodule (a lobectomy) is generally the preferred initial operation ^[19][20]. This provides the pathologist with the entire nodule to examine. While preserving the other half of your thyroid may allow you to avoid lifelong thyroid hormone medication, some people still require daily levothyroxine and blood test monitoring after a lobectomy ^[21][22].
• Total Thyroidectomy: Removing the entire thyroid may be considered for specific situations ^[23]. Your surgeon might recommend discussing this if you have clinically significant disease on both sides of your thyroid, if the goiter is very large, if it is causing severe compressive symptoms (trouble breathing/swallowing), or if molecular testing shows a high-risk mutation ^[24][2][25].

All surgeries carry risks, including bleeding, temporary or permanent voice-nerve injury, and—especially with total thyroidectomy—low calcium levels. Additionally, if you have a diagnostic lobectomy and the final pathology reveals a higher-risk cancer, a second “completion” surgery might be discussed ^[26].

Deciding what to do with a Bethesda III or IV nodule is a highly individualized, shared decision. By combining ultrasound results, molecular testing, your specific multinodular goiter anatomy, and your personal preferences, you can choose the path that balances safety and your quality of life.