Difference between familial and sporadic medullary thyroid carcinomas
The authors clearly conclude that there is no single morphologic criterion reliable for that distinction, although some findings tend to be more frequent in familial tumors. However, both diagnostic and biologic aspects would need additional comments for both C-cell hyperplasias (CCH) and MTCs. The presence of CCH is more frequently associated with, but not exclusive of, familial MTC. 2,3 Although the authors present a classic morphologic classification of CCH, 5 they do not draw any conclusion from that classification. The absence of CCH was found exclusive of sporadic MTC; the presence, however, was less informative.
Terminologically, two aspects need some clarification. First, focal and diffuse growth patterns are not fortunate descriptors. C-cell hyperplasia is always a focal process in the thyroid because it affects a certain number of follicles only. What can be focal is the follicular involvement. Probably focal and diffuse growth patterns would be better called segmental and circumferential when describing the follicular distribution. The second aspect is the term intraepithelial neoplasia. The expansile growth patterns of CCH share reproducible morphologic features, genetic and kinetic profiles consistent with C-CIN, but we do not have such an evidence for nonexpansile CCH yet. We would therefore propose to restrict the term C-CIN to expansile CCH only (nodular and neoplastic growth patterns).
All these data support the neoplastic transformation of C cells through multiple steps and the morphologic sequence of intraepithelial–invasive neoplasm.
Conclusion: The growth pattern of intraepithelial and invasive C-cell proliferation can provide clues on the familial background. Multifocal and bilateral invasive tumors associated with expansile intraepithelial C-cell neoplasm would be familial CCH MTC in 98.13% of cases, according with data presented by Kaserer et al. 3 The probability of being sporadic that neoplasm would be 0.1875 × (multifocal) × 0.2143 (bilateral) × 0.4643 (expansile CCH) = 0.0187, or 1.87%. Invasive MTCs still require the identification of tumors with metastatic potential; our personal experience and the Kaserer et al. data 3 suggest that neoplasms with desmoplastic stromal reaction have more likely acquired that potential and would be in so-called vertical growth phase.
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Published on 15 Nov 2012 - 14:30 (GMT)
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- Salvador J. Diaz-Cano
- Lisa Mears
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