What is the incidence of neuroendocrine tumors (NETs) (Neuroendocrine Tumors) histologically classified as T1N0M0 (TNM Classification) or below?

Incidence of T1N0M0 Neuroendocrine Tumors

The specific incidence of NETs classified as T1N0M0 or below is not directly reported in population-based registries, but can be estimated from overall NET incidence data combined with stage distribution patterns showing that approximately 7-15% of NETs present at stage I (which includes T1N0M0), translating to roughly 0.1-0.25 per 100,000 population annually.

Overall NET Incidence Context

The baseline incidence of all NETs has increased substantially over recent decades:

• Overall NET incidence reached 5.25 per 100,000 population per year by 2004 in the United States, representing a significant increase from 3.0 per 100,000 in earlier years 1
• The prevalence of NETs has been calculated at 35 per 100,000 population per year, with over 100,000 individuals living with NETs in the United States 1
• This rising incidence is primarily attributed to improved detection methods and diagnostic protocols rather than true increases in disease occurrence 1

Site-Specific Incidence Patterns

The distribution of NETs by anatomical site provides important context:

• Lung NETs: Combined incidence of 1.57 per 100,000 inhabitants, with typical carcinoids comprising 1-2% and atypical carcinoids only 0.1-0.2% of all pulmonary neoplasms 1
• Small intestinal NETs: 0.95 per 100,000 per year 1
• Rectal NETs: 0.86 per 100,000 per year 1
• Pancreatic NETs: 0.32 per 100,000 per year 1
• Gastric NETs: 0.30 per 100,000 per year 1

Stage Distribution at Presentation

The critical limitation is that most NETs present at advanced stages, making T1N0M0 tumors relatively uncommon:

• In midgut and hindgut NETs, only 7% present as stage I (which would include T1N0M0), with 8% as stage II, 19% as stage III, and 66% as stage IV 2
• Stage I patients demonstrate 100% 5-year survival, highlighting the excellent prognosis of truly localized disease 2
• The majority of NETs are diagnosed with either regional lymph node involvement or distant metastases already present 2, 3

Estimating T1N0M0 Incidence

Based on the available data:

• If overall NET incidence is 5.25 per 100,000 and approximately 7-15% present as stage I (depending on primary site), the estimated incidence of T1N0M0 NETs would be approximately 0.37-0.79 per 100,000 population annually
• This estimate varies significantly by primary tumor location, as appendiceal NETs have much lower metastatic rates (5% nodal, 2% hepatic) compared to ileal NETs (60% nodal, 30% hepatic) 4
• Bronchial carcinoids show relatively favorable early-stage presentation, with lower metastatic rates (15% nodal, 5% hepatic) compared to gastrointestinal sites 4

Important Clinical Caveats

Several factors complicate precise incidence determination:

• Many small, localized NETs are discovered incidentally during procedures performed for other indications, leading to potential underreporting in registry data 1
• The definition of T1 varies by anatomical site in the TNM classification system, making cross-site comparisons challenging 5, 2
• Improved imaging techniques (particularly somatostatin receptor imaging) are detecting smaller, earlier-stage tumors that would have been missed previously 1
• Population-based registries like SEER do not always capture complete TNM staging data for all cases, particularly for older diagnoses 3, 6