The following associations were observed in PTC and FTC combined: i) tumour size <2 cm with 14bpINS/INS (P = 0·030); ii) multicentricity with +3035CC (P = 0·030) and +3196GG (P = 0·030); iii) decreased thyroid HLA-G expression with +3196C and +3196CC; and iv) moderate HLA-G thyroid staining with UTR-2.
This assay will be useful for confirming the diagnosis of insulin-secreting tumor in patients suspected of recurrent fasting hypoglycemia and in physiologic studies of proinsulin secretion.
Tumors with malignant vs benign behavior showed less staining for insulin (3 of 7 vs 66 of 73; P = 0.015) and for proinsulin (3 of 6 vs 58 of 59; P < 0.001).
Of particular diagnostic value in this family was the determination of peripheral serum levels of proinsulin and C-peptide, which were used as tumour markers both for diagnosis and in the postoperative follow-up.
Analysis of the molecular forms of the proinsulin-derived peptides by high-performance liquid chromatography demonstrated that insulin was stored in the tumor as the intact peptide.
While insulinomas and proinsulin-secreting tumors have many physiologic parallels, these cases illustrate several key distinctions in their diagnosis and management.