Do thyroid tumors grow rapidly?

Growth Rate of Thyroid Tumors

The growth rate of thyroid tumors varies dramatically by histologic type: most differentiated thyroid cancers (papillary and follicular) grow very slowly over months to years, while anaplastic thyroid carcinoma grows extremely rapidly and is one of the most aggressive solid tumors in humans. 1

Differentiated Thyroid Cancer (Papillary and Follicular)

Slow, Indolent Growth Pattern

• Papillary microcarcinomas (≤1 cm) demonstrate minimal progression during active surveillance, with most remaining stable over years. 1 In Japanese surveillance studies, tumor growth ≥3 mm occurred in only a small minority of patients, with median time to growth of 25 months when it did occur. 1

• For papillary thyroid carcinomas, age is the primary predictor of growth rate during observation. 1 The 10-year estimated risk of significant tumor growth (≥3 mm) or lymph node metastasis is 36% in patients <30 years old, 14% in those aged 30-50, and only 6% in patients 50-60 years old. 1

• Most differentiated thyroid cancers are asymptomatic and detected incidentally, reflecting their slow growth that allows years of subclinical disease. 2 The overall 10-year survival for papillary carcinoma is 80-90% and follicular carcinoma 65-75%, consistent with indolent biology. 3

• Benign thyroid tumors (follicular adenomas) grow expansively rather than invasively, displacing adjacent structures while maintaining tissue planes. 4 This contrasts with malignant tumors that grow invasively. 4

Critical Size Thresholds

• Distant metastasis risk increases significantly once primary tumor size exceeds 20 mm (>T1 stage). 5 Below this threshold, the cumulative risk of distant spread remains low for both papillary and follicular carcinomas. 5

• Tumors >4 cm warrant total thyroidectomy regardless of other features, reflecting increased biological aggressiveness with larger size. 1

Anaplastic Thyroid Carcinoma (ATC)

Extremely Rapid, Aggressive Growth

• Anaplastic thyroid carcinoma is considered one of the most aggressive solid tumors in humans, with median survival of only 4 months after diagnosis. 1 Only 10-20% of patients survive 12 months, and long-term survival at 10 years is <5%. 1

• Over 40% of ATC patients present with large primary tumors (mean size 6 cm), gross extrathyroidal extension, and locoregional/distant metastases at diagnosis. 1 This reflects the tumor's rapid growth that quickly becomes clinically apparent. 1

• ATC typically presents with clinical symptoms rather than incidental detection, contrasting sharply with differentiated thyroid cancer. 1 Patients often have a history of rapidly enlarging neck mass. 1

• The disease-specific mortality for ATC approaches 100%, with fewer than 10% of patients younger than age 50 years at diagnosis. 1 The mean age at diagnosis is approximately 71 years. 1

Poorly Differentiated Thyroid Carcinoma

Intermediate Growth Rate

• Poorly differentiated carcinoma represents an intermediate category between well-differentiated and anaplastic thyroid cancer, characterized by invasion, mitoses >3, and necrosis. 1 These tumors grow more rapidly than differentiated cancers but slower than anaplastic carcinoma. 1

Clinical Implications

Surveillance vs. Immediate Intervention

• Active surveillance with ultrasound every 6-12 months is appropriate for unifocal papillary microcarcinomas (≤1 cm) without extrathyroidal extension or lymph node metastases. 1 This reflects the very slow growth rate that makes observation safe in selected patients. 1

• For tumors >1 cm, surgery is generally recommended as the growth rate, while slow, eventually leads to progression in most cases. 1, 2

Common Pitfall to Avoid

• Do not assume all thyroid cancers grow slowly—anaplastic carcinoma requires urgent multimodal treatment within weeks of diagnosis, as delays significantly worsen outcomes. 1 Staging must not delay definitive treatment in ATC. 1

• Aggressive variants of papillary thyroid carcinoma (tall cell, columnar, hobnail, solid) may behave more aggressively than classic papillary carcinoma despite the same histologic family. 6 These variants warrant closer surveillance and more aggressive initial management. 6