Lateral sentinel lymph node biopsy (SLNB) ensured a diagnostic accuracy of 100% in medullary thyroid cancer (MTC) patients based on final histopathology in a pilot study. 

“When we measured the diagnostic values of preoperative basal serum tumor markers, the values of lateral SLNB were superior to those of serum tumor markers,” said the authors of the study recently published in Head & Neck.

Out of the 16 MTC patients (median age, 52.2±12.1, range 33‑82, 68.7% female) included in the study, 14 (87.5%) did have sentinel lymph nodes (n=5.5±3.1) on the ipsilateral side of the primary tumor. From those, 3 (21.4%) presented lateral sentinel lymph node metastasis.


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Both frozen and histopathological analyses showed 100% specificity (11/11) and positive predictive value (2/2 and 3/3, respectively). However, histopathological analysis performed better than frozen analysis regarding sensitivity (100%, 3/3 vs 66.7%, 2/3) and negative predictive value (100%, 11/11 vs 91.6%, 11/12).

Lateral SLNB achieved superior diagnostic accuracy compared to the conventional tumor markers calcitonin and carcinoembryonic antigen (CEA). For serum calcitonin levels in male and female patients, the values were calculated as follows: sensitivity – 100% (1/1) and 50% (1/2); specificity – 50% (2/4) and 44.4% (4/9); positive predictive value – 33.3% (1/3) and 16.7% (1/6); and negative predictive value – 100% (2/2) and 80% (4/5). The sensitivity and positive predictive value of CEA was 0% (0/2), while the specificity and negative predictive value was 71.4% (5/7).

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SLNB was performed by injecting the radioisotope (55.5 MBq technetium (Tc)-99m phytate in 0.1‑0.2 mL saline) into the primary tumor, preoperatively, under ultrasound guidance. Probed lymph nodes were then detected using a collimated gamma probe, excised, and sent for both frozen and histopathological analyses. 

A total of 82 lateral sentinel lymph nodes were dissected at levels II‑V following the modified radical neck dissection type III. Lateral sentinel lymph nodes were primarily found in ipsilateral neck level III, while metastases, detected in 7.3% (6/82), were mostly (66.7%) observed in level IV.

Besides transient postoperative hypocalcemia, the authors reported no perioperative complications and no recurrence during follow-up (median, 34 months, range 7‑75 months). However, the authors recognized that it is still unknown whether multiple site SLNB will impact surgical outcomes and increase procedure-associated morbidity.

Though preliminary and limited by the small number of patients, this study is promising in showing the potential surgical value of SLNB in detecting occult lateral lymph node metastases in clinically lateral lymph node-negative MTC patients.

Reference

Kim MJ, Back K, Choe J-H, Kim J, Kim JS. Feasibility of lateral sentinel lymph node biopsy in medullary thyroid cancer: a surrogate tool for determining prophylactic lateral neck dissection—A pilot study. Head Neck. Published online July 20, 2021. doi:10.1002/hed.26808