Utility of bone scans in patients with RCC

Introduction: Technetium-99m-disphosphonate bone scintigraphy is often used for evaluation of renal cell carcinoma(RCC) osseous metastases. Given that the majority of RCC osseous metastases are osteolytic, the sensitivity for bone metastases detection by bone scintigraphy is < 50% as bone scans only depict the osteoblastic reaction of bone metastases. Strictly osteolytic RCC metastases cannot be imaged by scintigraphy thus making false negatives on bone scintigraphy common. While scintigraphy has a known low sensitivity for RCC metastases, we hypothesize that bone scintigraphy is nonetheless able to detect new osseous metastases not otherwise reported on prior radiographic or cross sectional imaging.

Methods: Adult patients with RCC were evaluated for bony metastases by osseous scintigraphy from 12/16/2004 to 7/15/2021. We solely analyzed patient’s very first bone scan whether that bone scan was an initial staging bone scan or performed later in the patient’s disease course. Bone scan findings were corroborated with cross sectional imaging or radiographs that were performed within three months from the initial bone scan. A true positive result was given if all metastatic lesions reported on bone scan were consequently seen on CT or radiography. A true negative result was given if no lesions were seen on bone scan or CT. A bone scan was deemed a false negative if any lesion that was depicted on CT was not reported by bone scan. A bone scan was considered a false positive if a lesion was reported as a metastasis or suspicious for metastases and not subsequently seen on follow up cross sectional or radiographic imaging.

Results: Of the 86 patients with RCC evaluated by bone scan, 73 patients were included for analysis. Any patient with a secondary malignancy in addition to RCC was omitted from the study. There were 3 additional patients that were also not included as they did not have any follow up cross sectional or radiographic imaging to corroborate reported bone scan findings. Of the 73 patients sampled, there was a male predominance and predominance of clear cell histology. Overall, osseous scintigraphy had a sensitivity of 51.6% and specificity of 89.1 with a Chi-Square p-value <0.001. Bone scans had a positive predictive value of 73.7% and negative predictive value of 75.9%.

Only 10 bone scans of the 73 bone scans reported a lesion suspicious for metastases that was not otherwise previously or concurrently reported by CT. Of these 10 bone scans, 5 were deemed a false positive and did not have a corroborating suspicious radiographic or cross sectional finding. In all, only 3 total scintigraphic studies depicted new lesions suspicious for metastases that were not previously seen on CT or radiograph.

Conclusions: Contrary to our initial postulation, osseous scintigraphy does not appear to have added clinical value by detecting osseous lesions not otherwise previously characterized by CT or radiograph in asymptomatic patients. In only 4% of the cases (3 of 73) was a metastatic lesion depicted scintigraphically that had not previously been seen by CT or radiograph. In one of these cases, only a single metastatic lesion in the lesser trochanter was missed by CT and although lesion was seen scintigraphically it overall did not change the patient’s management as additional lesions were seen by both CT and bone scan. Lastly, the remaining two patients with new true positive findings seen scintigraphically were experiencing bony pain at the time of bone scan. In turn, the bone scans for these two patients were indicated as per interdisciplinary consensus guidelines. Current interdisciplinary consensus guidelines do not recommend specific screening for bone metastases in asymptomatic patients aside from routine tumor staging by CT Chest, Abdomen and Pelvis. Ultimately, our findings do not support the use of bone scan in asymptomatic patients given the low sensitivity of bone scan and lack of significant additional osseous findings detected by bone scan in asymptomatic patients.

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