What to do now

1. Review the complete histopathology and operative details Confirm:
   • Exact tumor size and whether this is truly papillary thyroid microcarcinoma, pT1a
   • Multifocality
   • Microscopic or gross extrathyroidal extension
   • Lymphovascular invasion
   • Margins
   • Number, size, and extranodal extension of any lymph-node metastases
   • Aggressive histologic subtype, if any
   A solitary intrathyroidal classic PTC <1 cm with no nodal disease or adverse features is generally ATA low recurrence risk. For such a case, routine RAI is not recommended.
2. Repeat biochemical assessment at 6-12 weeks postoperatively Measure, preferably in the same laboratory:
   • Serum Tg
   • Anti-thyroglobulin antibodies (TgAb) with every Tg measurement
   • TSH
   • Free T4 as needed
   Interpretation depends heavily on whether the Tg of 30 was:
   • measured while hypothyroid or TSH-stimulated, or
   • measured on levothyroxine with a suppressed/normal TSH.
   TgAb positivity can make Tg falsely low or unreliable. Tg trends and TgAb trends then become more useful than a single Tg value.
3. Perform a high-quality neck ultrasound Assess the thyroid bed and central/lateral cervical lymph-node compartments for residual disease or nodal metastases. A high Tg with a suspicious node should lead to US-guided FNA, with Tg washout where appropriate.
4. Do not label it low-risk/excellent response if Tg remains high In patients treated with total thyroidectomy but no RAI, the 2025 ATA response framework considers a non-stimulated Tg >5 ng/mL with no structural lesion as a biochemical incomplete response, not an excellent response. A Tg of 30, if confirmed at the appropriate postoperative interval and with negative TgAb, needs evaluation for:
   • substantial benign thyroid remnant
   • occult cervical nodal disease
   • less commonly, distant iodine-avid disease
5. RAI decision should follow the reassessment, not the early Tg alone
   • If repeat Tg becomes low and ultrasound is reassuring, manage with levothyroxine, appropriate TSH target, and surveillance. No routine RAI for a true low-risk microcarcinoma.
   • If Tg remains clearly elevated, especially around 30 ng/mL, rises over time, or imaging shows disease, refer to an endocrinology and nuclear-medicine thyroid cancer multidisciplinary team for structural staging and consideration of RAI as adjuvant therapy or treatment for demonstrated persistent disease.
   • If structural disease is found in the neck, surgery is usually considered for resectable nodal disease rather than using RAI as a substitute for removal of significant nodal disease.

Practical interpretation for this case

Repeat Tg, TgAb, and TSH at 6-12 weeks; obtain expert neck ultrasound; review pathology for adverse features. Do not automatically administer RAI solely because of this early postoperative Tg.

• Small-cell/neuroendocrine prostate carcinoma often has low or absent PSMA expression, so a PSMA scan can be falsely negative or underestimate disease.
• It is usually aggressive, high-grade, glycolytically active, and may show visceral and lytic bone metastases, making it typically FDG-avid.
• PSA can be low despite a large disease burden, so conventional PSA-driven PSMA imaging can be misleading.

Practical approach

• Preferred PET scan: ^18F-FDG PET-CT
• Also obtain conventional staging appropriate to the presentation, commonly contrast-enhanced CT chest/abdomen/pelvis or MRI pelvis. Consider brain MRI if there are neurologic symptoms or extensive disease, because CNS involvement can occur.
• PSMA PET-CT can be added selectively if pathology is mixed adenocarcinoma plus small-cell carcinoma, if there is known PSMA-avid disease, or if PSMA-targeted therapy is being considered. It should not replace FDG PET in pure small-cell disease.