S-100 protein positive (sustentacular) cells in pulmonary carcinoid tumorlets: a quantitative study of 24 cases.

Stellate-shaped S-100 protein positive sustentacular cells (SCs) appear to correlate inversely with the degree of tumor malignancy in some neuroendocrine tumors. Therefore, the SCs have been investigated in carcinoid pulmonary tumorlets and subsequently examined quantitatively in order to provide a basis for estimation of this phenomenon in tumorlet related lesions, especially carcinoids and neuroendocrine carcinomas. Pulmonary tissue from twenty-four patients with carcinoid tumorlets was studied immunohistochemically for S-100 protein positive SCs together with glial fibrillary acidic protein, actin, desmin, vimentin and cytokeratins. Tumorlet SCs were calculated per 10,000 tumorlet elements. The presence of SCs was proven in 18 subjects (75%) of all examined cases with quantitative frequency between 13 and 196 SCs per 10,000 tumorlet elements. The histogram showed three separate clusters of cases. Cluster 2 and cluster 3 with strikingly high frequency of SCs, i.e. from 66 up to 196 SCs per 10,000 tumorlet cells, may represent the biphasic differentiation potential of tumorlet elements. The mentioned lesions could be regarded as the possible precursors of pulmonary paragangliomas or paraganglioid carcinoids.