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).
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.
While insulinomas and proinsulin-secreting tumors have many physiologic parallels, these cases illustrate several key distinctions in their diagnosis and management.
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.
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.
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.