Figure 12. TgAb Effects on Serial Tg IMA and Tg RIA Measurements. Serial TgAb, Tg-RIA and Tg-IMA measurements made in two DTC patients who underwent a change in TgAb status (panel A, positive to negative) or (panel B negative to positive) before death from structural DTC. These cases illustrate why a Tg measurement cannot be interpreted without knowing the TgAb status of the patient (57). The de novo appearance of TgAb (Patient B) either reflects a change in tumor-derived Tg heterogeneity (secretion of a more immunogenic Tg molecule), or recognition of tumor-derived Tg by the immune system. In contrast, TgAb can become undetectable despite the exacerbation of disease (Patient A).