Medullary thyroid carcinoma is not the common papillary variety that dominates thyroid cancer statistics and fuels much of the active surveillance debate. It arises from the parafollicular C cells of the thyroid, the cells that produce calcitonin, and it behaves differently from its more indolent cousins. It does not respond to radioiodine therapy, it secretes measurable biomarkers that track its burden, and it can metastasize to cervical lymph nodes early in its course. When such a tumor is caught while still under one centimeter in diameter, it earns the designation of microcarcinoma, and it is precisely in this small, seemingly harmless form that the disease increasingly presents. As ultrasound technology improves and thyroid imaging becomes more common, more of these minute tumors are being found, and clinicians are left with a growing population of patients for whom the natural history is poorly charted.

The research team, led by Yuanmeng Li, Naishi Li, Weigang Zhao, and Xiaolan Lian, combed through their institutional records and identified 75 cases of medullary thyroid microcarcinoma. Within that group, they focused on a subset of 20 patients whose diagnosis and surgical treatment had been delayed and for whom baseline ultrasound imaging of adequate quality existed. For these patients, the observational period before surgery exceeded six months, with a median duration of 27 months. That is a substantial stretch of time for a tumor to do whatever it is going to do, and it gave the investigators a rare longitudinal window into the behavior of an entity that is usually excised quickly and studied only in retrospect.

What the ultrasound scans revealed was striking. Seventy-five percent of the delayed-surgery patients, 15 of the 20, showed sonographic evidence that their microcarcinoma nodules had grown during the observation period, a proportion with a 95 percent confidence interval spanning roughly 53 to 89 percent. When the researchers compared the final nodule volumes with the initial measurements, the difference was statistically robust, with p values below 0.001. In plain terms, these were not static lesions idling in the thyroid gland. During a median of more than two years without intervention, the majority of these tumors expanded, and the volume change was unmistakable rather than a borderline statistical artifact.

Growth alone, however, does not tell a clinician whether a tumor has become more dangerous. To address that question, the team turned to the pathological and biochemical signatures that medullary thyroid carcinoma leaves behind. They stratified their patients using a 5 millimeter threshold, a cut point that divides the microcarcinoma range into its smallest and largest halves. The results were consistent across every measure they examined. Tumors larger than 5 millimeters were associated with higher preoperative levels of calcitonin and carcinoembryonic antigen, the two biomarkers that serve as the workhorses of medullary thyroid cancer surveillance. They also carried a greater incidence of lymph node metastasis, more advanced TNM staging, and a lower rate of biochemical cure after surgery, meaning a lower likelihood that postoperative biomarker levels fell to undetectable territory. Every one of these comparisons reached statistical significance at p values below 0.01.

Correlation analysis reinforced the same story along a continuous gradient rather than a binary divide. Tumor size in this cohort was positively associated with preoperative calcitonin levels, with a correlation coefficient of 0.357 and a p value of 0.022, and with carcinoembryonic antigen levels, which showed an even stronger association at r equals 0.428 and p equals 0.003. Size also correlated with lymph node metastasis at r equals 0.388, with TNM stage at r equals 0.416, and with worse overall outcome at r equals 0.330, the latter with a p value of 0.006. None of these correlations is overwhelming in isolation, and the study’s own authors are careful to note that tumor size and observation time are intertwined in this setting, making it impossible to fully disentangle whether the tumors that grew were intrinsically more aggressive or whether the passage of time itself allowed indolent lesions to progress. But the direction of every association points the same way: bigger tumors, in this disease, mean more disease.

The biological logic behind these findings is worth unpacking. Calcitonin secretion is a function of the number of malignant C cells present, so a growing tumor should, and does, produce a rising biomarker signal. Cervical lymph node metastasis in medullary thyroid carcinoma is known to correlate with primary tumor size, and the 5 millimeter threshold identified here aligns with a broader literature suggesting that risk in this disease accrues continuously rather than in discrete jumps. What makes the new study notable is not that it overturns established biology but that it documents the temporal dimension directly. Most of what is known about medullary thyroid microcarcinoma comes from surgical specimens examined after the fact, snapshots of tumors at the moment of removal. Watching these tumors across a median of 27 untreated months provides something those snapshots cannot: evidence that the clock matters.

The clinical context amplifies the significance. Active surveillance, the strategy of monitoring small thyroid nodules with serial ultrasound rather than operating immediately, has gained genuine traction for papillary thyroid microcarcinoma, where large Japanese cohort studies have shown that the majority of these lesions never grow to a clinically meaningful size. That evidence base has created a certain cultural momentum, a sense among some patients and clinicians that small thyroid cancers in general can be watched safely. The new findings are a pointed reminder that medullary thyroid carcinoma is a different biological entity. There is no equivalent evidence base supporting surveillance for medullary microcarcinoma, and this study now provides the first direct, if retrospective and limited, evidence that waiting carries measurable risk. The authors stop short of claiming that every microcarcinoma will progress, and indeed a quarter of their delayed-surgery cohort showed no growth, but the burden of proof has shifted.

Several caveats deserve honest acknowledgment. The study is retrospective and comes from a single center, which means selection bias is a real possibility; the very fact that these patients experienced delayed diagnosis and surgery suggests their tumors may have been clinically silent or initially mischaracterized, a circumstance that may not generalize to all microcarcinomas. Twenty patients is a small sample, and the confidence intervals around the 75 percent growth figure are correspondingly wide. The authors themselves note that the clinical implications of their findings require confirmation in future studies, ideally prospective ones with standardized imaging intervals and larger, multi-center cohorts. The study was approved by the Ethics Committee of Peking Union Medical College Hospital and conducted in accordance with the Declaration of Helsinki, and it was supported by funding from the Chinese Academy of Medical Sciences, the National Natural Science Foundation of China, and related institutional programs, lending it institutional credibility even as its scale remains modest.

Even with those limitations, the message for clinical practice is difficult to ignore. Medullary thyroid microcarcinoma should not be presumed to remain stable during an untreated interval, the authors conclude, and once the diagnosis is suspected, prompt workup and timely surgery are the prudent default. For a disease that announces itself through calcitonin and CEA, biomarkers that can be measured with a simple blood draw, and that can be imaged with the ultrasound machines already present in every endocrinology clinic, the barriers to early action are low. What this study adds is the urgency: in the roughly two years that separated baseline imaging from surgery for these patients, three quarters of their tumors grew, and the ones that grew larger arrived at the operating room with higher biomarker levels, more nodal disease, more advanced staging, and poorer chances of biochemical cure. Small, in medullary thyroid cancer, does not mean stationary, and the new data suggest that the window in which these tumors are truly micro may be one worth closing deliberately rather than watching drift by.

Subject of Research: Tumor growth and outcomes in medullary thyroid microcarcinoma during delayed surgery

Article Title: Tumor growth in medullary thyroid microcarcinoma during delayed surgery: a single-center study

Article References: Li, Y., Chai, X., Liu, H., Zhang, H., Li, X., Li, B., Chen, X., Zhou, J., Li, N., Zhao, W., & Lian, X. (2026). Tumor growth in medullary thyroid microcarcinoma during delayed surgery: a single-center study. BMC Endocrine Disorders. https://doi.org/10.1186/s12902-026-02606-2

Image Credits: AI Generated

DOI: 10.1186/s12902-026-02606-2

Keywords: medullary thyroid microcarcinoma, thyroid cancer, tumor growth, calcitonin, carcinoembryonic antigen, lymph node metastasis, delayed surgery, active surveillance, ultrasound, TNM staging, biochemical cure, endocrine disorders

The patient at the center of the report was a 64-year-old woman with a history of diabetes mellitus, hypertension, and chronic kidney disease. She had no complaints whatsoever, no palpable thyroid nodule, no swollen lymph nodes, and no family history of thyroid cancer or other endocrine tumors. Her medullary thyroid carcinoma came to light only because an unrelated metabolic work-up revealed an isolated elevation of procalcitonin, a biomarker more commonly associated with severe bacterial infections. That incidental finding set in motion a diagnostic chain that ultimately uncovered a two-centimeter tumor in her left thyroid lobe, along with a second, entirely separate and unexpected cancer measuring just half a millimeter in the right lobe.

The diagnostic challenge in this case was considerable, and it illustrates why medullary thyroid carcinoma remains one of the most treacherous diagnoses in endocrinology. Roughly one quarter of cases arise in the setting of inherited syndromes such as multiple endocrine neoplasia type 2A and 2B or familial medullary thyroid carcinoma, all driven by germline mutations in the RET proto-oncogene. The majority of cases, however, are sporadic, and somatic RET mutations are found in about sixty percent of these tumors. The specific mutation involved matters enormously: the common p.Met918Thr alteration produces a markedly more aggressive course, while RET-negative tumors often carry RAS-family mutations instead. Because family history can be absent in up to half of hereditary cases, guidelines recommend germline RET screening even in patients who appear to have sporadic disease. In this particular patient, germline testing could not be performed, leaving an open question about whether an occult hereditary syndrome might have been at play.

Laboratory evaluation told an intriguing story. The woman’s serum calcitonin—the classic hallmark of C-cell derived tumors—measured 2100 nanograms per liter, and her carcinoembryonic antigen, or CEA, a glycoprotein used as a tumor marker, stood at 20.8 nanograms per milliliter. Yet neither of these values had triggered the initial investigation. Instead, it was procalcitonin that raised the alarm, and the report’s authors emphasize that this was no accident. Procalcitonin secretion is a recognized physiological product of thyroid parafollicular C cells, so once a C-cell neoplasm is present, its elevation is expected rather than surprising. In this patient, the procalcitonin signal happened to arrive first, in a clinical context—chronic kidney disease—where such an elevation could easily have been dismissed or misattributed.

The authors argue that the concurrent CEA elevation was actually the more diagnostically instructive finding. CEA is not specific to C cells, and an unexplained CEA rise in an older adult is conventionally pursued as a possible sign of gastrointestinal malignancy. Several previous reports have described medullary thyroid carcinoma presenting initially as an isolated CEA elevation that was ultimately traced back to the thyroid. In one directly comparable case, a patient with subclinical hyperthyroidism was found to have sporadic medullary thyroid carcinoma first suspected because of a high CEA level, with strong CEA immunoreactivity later confirmed on the surgical specimen. Larger retrospective series have also shown that preoperative CEA correlates with tumor size and stage, with concentrations above roughly 270 to 400 nanograms per milliliter associated with larger or metastatic disease. The modest CEA elevation in this new case fits neatly with the small, low-grade, node-negative tumor that pathology ultimately revealed.

Chronic kidney disease complicated the interpretation at every turn. Reduced renal clearance can independently cause mild elevations of both calcitonin and CEA, which means that in a patient like this, both markers could have been dismissed as artifacts of her kidney function. The report’s authors stress that calcitonin elevation in chronic kidney disease should never be reflexively attributed to impaired renal clearance alone, because excluding an underlying C-cell malignancy remains essential. Their message is a warning against a common diagnostic shortcut: in patients with kidney disease, an elevated calcitonin level demands the same rigorous work-up it would receive in anyone else, including neck imaging, fine-needle aspiration with calcitonin measurement in the washout fluid, and appropriate immunocytochemistry.

That work-up, in this case, was thorough. Neck ultrasonography showed solid hypoechoic nodules in both lobes. Fine-needle aspiration of the left lobe nodule was consistent with medullary thyroid carcinoma, with calcitonin detected in the needle washout and immunocytochemistry showing positivity for chromogranin A and CEA alongside negativity for thyroglobulin—the protein made by ordinary thyroid cells, whose absence helps distinguish medullary from other thyroid cancers. Computed tomography of the neck, thorax, and abdomen found no distant metastases, and a gallium-68 DOTATATE PET/CT scan, which images somatostatin receptor expression, showed uptake in the thyroid nodule and several cervical and axillary lymph nodes. The patient underwent total thyroidectomy with bilateral central neck dissection, and the surgery went without complication.

Pathology confirmed a two-centimeter, partially encapsulated, low-grade medullary thyroid carcinoma with negative surgical margins, no vascular or perineural invasion, and a Ki-67 proliferation index of just one percent. All seventeen dissected lymph nodes were free of metastasis. Tumor cells stained positive for calcitonin, CEA, chromogranin A, synaptophysin, and several other markers, with loss of CD56 expression. Interestingly, amyloid deposition—a classic pathological feature of medullary thyroid carcinoma—could not be demonstrated. And in a remarkable twist, an incidental 0.05-centimeter classic papillary microcarcinoma, an entirely different type of thyroid cancer, was found in the right lobe. After surgery, the patient’s biomarkers collapsed dramatically: calcitonin fell from 2100 to 3.1 nanograms per liter and CEA from 20.8 to 3.1 nanograms per milliliter, and at three-month follow-up she remained well.

Beyond this single patient, the report situates the case within a rapidly evolving field. Recent studies show that calcitonin’s immunohistochemical specificity is not absolute—calcitonin-positive staining in lung tissue has occasionally masqueraded as metastatic medullary thyroid carcinoma when the real lesion was a pulmonary neuroendocrine tumor. Research on imaging decisions suggests that a 500 picograms-per-milliliter calcitonin threshold for staging scans has high sensitivity but low specificity, and that models combining calcitonin with ultrasound findings of suspicious lymph nodes perform better than any single value. On the surgical side, data from nearly 400 patients indicate that lobectomy may be a safe option in selected sporadic cases without germline RET mutations, whereas total thyroidectomy remains essential in hereditary disease. For advanced cases, a network meta-analysis found that the selective RET inhibitor selpercatinib reduced the risk of progression by ninety percent compared with placebo, outperforming older multikinase inhibitors in both efficacy and tolerability, though acquired resistance through solvent-front mutations remains an emerging challenge.

The broader lesson from this case is that medullary thyroid carcinoma can remain entirely silent until an incidental biochemical abnormality—here an isolated procalcitonin elevation rather than the expected calcitonin trigger—prompts further evaluation. For clinicians managing patients with chronic kidney disease, the message is unambiguous: biomarker elevations deserve careful, layered interpretation rather than reflexive attribution to renal impairment. As the field moves toward individualized medicine built on genetics, organoid models, and refined imaging strategies, cases like this one serve as a reminder that the first step in precision oncology is often the oldest one—paying close attention to an abnormal number on a routine laboratory report, and refusing to stop until its meaning is fully understood.

Subject of Research: A case of asymptomatic medullary thyroid carcinoma presenting with isolated procalcitonin elevation in a patient with chronic kidney disease

Article Title: Asymptomatic Medullary Thyroid Carcinoma With Isolated Carcinoembryonic Antigen Elevation in a Patient With Chronic Kidney Disease: A Case Report

Article References: Altınyüzük, O., Ediz, B., Yalın, S. F., & Parmaksız, E. (2026). Asymptomatic Medullary Thyroid Carcinoma With Isolated Carcinoembryonic Antigen Elevation in a Patient With Chronic Kidney Disease: A Case Report. Clinical Case Reports, 14(9), Article e73580. https://doi.org/10.1002/ccr3.73580

Image Credits: AI Generated

DOI: 10.1002/ccr3.73580

Keywords: medullary thyroid carcinoma, procalcitonin, calcitonin, carcinoembryonic antigen, chronic kidney disease, RET proto-oncogene, thyroidectomy, biomarkers, neuroendocrine tumors, fine-needle aspiration, selpercatinib, case report