Surgical Pathology Criteria–

Thymic Well Differentiated Neuroendocrine Carcinoma (Carcinoid and Atypical Carcinoid)

Differential Diagnosis

Thymoma Thymic Carcinoid / Well Differentiated Neuroendocrine Carcinoma
Immature T cells present Mature T and B cells may be present, but lacks immature T cells
Punctate necrosis very rare Punctate necrosis in nearly all cases
Neuroendocrine markers negative (except CD57) Neuroendocrine markers positive
Rosettes and glands/pseudoglands may be seen in both carcinoid and type A thymoma

 

Thymic Carcinoma Thymic Carcinoid / Well Differentiated Neuroendocrine Carcinoma
Cytologically malignant Uniform cells, at most mildly atypical
Punctate necrosis very rare Punctate necrosis in nearly all cases
Neuroendocrine markers negative (except CD57) Neuroendocrine markers positive
Both may have high mitotic rates

 

Metastatic Carcinoid of Lung Thymic Carcinoid / Well Differentiated Neuroendocrine Carcinoma
History and imaging may reveal primary site History and imaging should reveal no other primary site
TTF1 positive in >90% of lung carcinoids TTF1 negative (few tested)

 

Paraganglioma Thymic Carcinoid / Well Differentiated Neuroendocrine Carcinoma
Keratin negative Keratin positive
Punctate necrosis very rare Punctate necrosis in nearly all cases
Both are positive for neuroendocrine markers and may have sustentacular cells

 

Thymic Poorly Differentiated Neuroendocrine Carcinoma Thymic Carcinoid / Well Differentiated Neuroendocrine Carcinoma
Nearly always cytologically malignant Uniform cells with at most mild atypia
No clear cutoff is defined between these two

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