Estimating the Growth Rate of Lung Metastases in Differentiated Thyroid Carcinoma: Response Evaluation Criteria in Solid Tumors or Doubling Time?

Prognostic value of tumor volume doubling time in lung-metastatic adenoid cystic carcinoma

OBJECTIVES

Lung metastases in adenoid cystic carcinoma (ACC) usually have indolent growth and the optimal timing to start systemic therapy is not established. We assessed ACC lung metastasis tumor growth dynamics and compared the prognostic value of time to progression (TTP) and tumor volume doubling time (TVDT).

METHODS

The study included ACC patients with ≥1 pulmonary metastasis (≥5 mm) and at least 2 chest computed tomography scans. Radiology assessment was performed from the first scan showing metastasis until treatment initiation or death. Up to 5 lung nodules per patient were segmented for TVDT calculation. To assess tumor growth rate (TGR), the correlation coefficient (r) and coefficient of determination (R2) were calculated for measured lung nodules. TTP was assessed per RECIST 1.1; TVDT was calculated using the Schwartz formula. Overall survival was analyzed using the Kaplan-Meier method.

RESULTS

The study included 75 patients. Sixty-seven patients (89%) had lung-only metastasis on first CT scan. The TGR was overall constant (median R2 = 0.974). Median TTP and TVDT were 11.2 months and 7.5 months. Shorter TVDT (<6 months) was associated with poor overall survival (HR = 0.48; p = 0.037), but TTP was not associated with survival (HR = 1.02; p = 0.96). Cox regression showed that TVDT but not TTP significantly correlated with OS. TVDT calculated using estimated tumor volume correlated with TVDT obtained by segmentation.

CONCLUSION

Most ACC lung metastases have a constant TGR. TVDT may be a better prognostic indicator than TTP in lung-metastatic ACC. TVDT can be estimated by single longitudinal measurement in clinical practice.

Second radioiodine treatment hardly benefits TT-DTC patients with radioiodine-negative metastases on initial post-therapeutic whole-body scans

BACKGROUND

The effect of second 131I treatment (RT) in totally thyroidectomized differentiated thyroid cancer (TT-DTC) patients with true-positive thyroid beds and false-negative metastasis (TB+/M-) on initial post-therapeutic whole-body scan (Rx-WBS) remains unknown.

METHODS

TT-DTC patients with TB+/M- on initial Rx-WBS receiving and not receiving second RT were categorized into group A and group B, respectively, while patients with 131I-avid metastasis receiving second RT were referred to as group C. Biochemical remission (BR) was defined as a decrease of ≥25.0% in thyrotropin-suppressed thyroglobulin (Tgon) level, while the structural response (SR) was determined by the change in the size of the largest lesion.

RESULTS

In total, 145 patients were eligible. In group A, the median Tgon measured 3.3 ng/mL before and 3.0 ng/mL at 4 months after second RT (P=0.307), yielding a decrease in the median Tgon (∆Tgon%) of 13.3%, a BR rate of 36%, and an insignificant SR, which were comparable to those in group B. In group C, however, a median ∆Tgon% of 37.8% and a BR rate of 64% were obtained, which were significantly higher than those in group A (P=0.038 and 0.022, respectively), with SR distributions similar to those in group A. In addition, 131I uptake in the neck was not statistically associated with the detection of metastasis on initial Rx-WBS.

CONCLUSIONS

This controlled study demonstrated a subtle response to second RT in TT-DTC patients with TB+/M- on initial Rx-WBS, representing a meaningful advancement in avoiding ineffective repeated RT.