Patients with small cell lung cancer (SCLC) often fail to respond to chemotherapy due to multidrug resistance (MDR). Technetium-99m-MIBI was reported to be a suitable transport substrate of P-glycoprotein, which is a cytoplasmic membrane protein encoded by the MDR gene. The purpose of this study was to evaluate whether or not the degree of MIBI uptake in SCLC or its retention on delayed imaging correlated with response to chemotherapy.
Methods: Twenty-five patients (19 men, 6 women; mean age 59 +/- 10 yr) with biopsy-proven SCLC had MIBI SPECT 3-7 days before starting chemotherapy. Imaging was acquired 1 and 4 hr after injection of 740 MBq MIBI using a single-head rotating gamma camera. Tumor-to-normal lung uptake ratio (T/NL) was measured. Percent retention (%R) was measured as: %R = 100 x (T/NL at 4 hr)/(T/NL at 1 hr). All patients received VAP chemotherapy (VP-16 100 mg/m2, adriamycin 40 mg/m2, cisplatin 25 mg/m2) every 4 wk for at least three times. Response to chemotherapy was grouped as complete remission, partial remission and no remission according to the change of tumor size on chest radiograph and CT images. Differences in T/NL and %R among the three groups were analyzed using ANOVA.
Results: T/NL of patients with complete remission (n = 7) and partial remission (n = 10) were significantly higher than that of no remission (n = 8) in 1 hr and 4 hr. T/NL at 1 hr in three groups were 2.75 +/- 0.78, 2.35 +/- 0.31 and 1.65 +/- 0.36, respectively. T/NL at 4 hr in three groups was 2.61 +/- 0.94, 2.48 +/- 0.50 and 1.66 +/- 0.42, respectively. However, %R was not different among three groups. Percent retention in three groups was 109.40 +/- 22.10, 96.71 +/- 14.25 and 103.59 +/- 28.43, respectively.
Conclusion: SCLC with a higher MIBI uptake was more likely to respond to chemotherapy than that with a lower uptake. However, there was a considerable overlap of MIBI uptake among subjects. No significant correlation between the MIBI retention between 1 hr and 4 hr, and the response to chemotherapy was noted.