CT Unreliable for Predicting Future Liver Metastases in Breast Cancer Patients
Abstract & Commentary
Synopsis: Despite theoretical considerations and some preliminary evidence suggesting that helical CT of the liver can identify patients with breast cancer who will subsequently develop liver metastases, helical CT currently cannot be used to reliably make this distinction in individual patients.
Source: Sheafor DH, et al. Hepatic parenchymal enhancement during triple-phase helical CT: Can it be used to predict which patients with breast cancer will develop hepatic metastases? Radiology 2000;214:875-880.
Radiologists at duke university medical center performed triple-phase (precontrast, arterial-dominant phase, and portal venous-dominant phase) helical CT of the liver in 60 patients with known breast cancer but no liver metastases visible at CT. They measured the peak hepatic attenuation values and the amount of hepatic enhancement, as well as the hepatic attenuation values and enhancement present at 25 and 30 seconds in each patient. Hepatic attenuation ratios (hepatic attenuation at 25 and 30 seconds divided by peak hepatic attenuation) and enhancement ratios (hepatic enhancement at 25 and 30 seconds divided by peak hepatic enhancement) were calculated.
Eighteen (30%) of the 60 patients developed hepatic metastases during the follow-up period (mean follow-up, 18 months). In this group, hepatic attenuation and enhancement ratios at 25 and 30 seconds were higher than in the group of patients that did not develop liver metastases (P < 0.05). However, after correction for the timing of chemotherapy, there were no statistically significant differences in the hepatic parameters between the two groups of patients. Moreover, there was considerable overlap of the parameters between the groups. With an enhancement ratio at 30 seconds of 0.4 as the threshold, the specificity of the technique was 92%, but the sensitivity was only 28% and the accuracy was 55%. Sheafor and associates conclude that this technique, as implemented currently, cannot be used to predict which individual patients with breast cancer will develop liver metastases.
COMMENT BY DAVID M. PANICEK, MD
Because the presence of metastases within the liver is known to be associated with an overall increase in hepatic arterial blood flow, studies have been performed to determine whether micrometastatic liver disease can be detected by demonstrating such increased blood flow before macroscopic metastases become visible at imaging. Such detection could allow earlier or different therapy to be initiated, with potentially improved patient outcome. The findings of one study1 suggested that cancer patients at increased risk of subsequently developing hepatic metastases from a variety of tumors could be identified at dual-phase helical CT by an increase in hepatic arterial perfusion compared to the perfusion measured in patients who did not develop hepatic metastases.
Unfortunately, the current study was unable to confirm those findings for individual patients. This is perhaps not surprising, given the complex nature of biological systems. Patient weight, prandial status, and other coexistent hepatic disease (including fatty infiltration) can influence hepatic CT attenuation values. Additionally, differences in cardiac output could have a major effect on hepatic enhancement at specified times after contrast administration.
The patients in this study who ultimately developed overt liver metastases did not undergo biopsy at the time of initial CT, so it is not known if micrometastases were already present at that time. Therefore, it is not clear whether altered hepatic hemodynamics cause hepatic metastases to develop (by providing a more vascular, "fertile soil" in which metastases can grow), or whether they are caused by the presence of micrometastatic disease. Even allowing that micrometastatic disease could actually increase hepatic arterial blood flow, it is likely that the presence of only a small amount of micrometastatic disease in the liver would limit the ability of helical CT to demonstrate associated changes in hepatic perfusion. Future advances, possibly in molecular imaging, will be required to achieve the "holy grail" of detecting micrometastatic disease in individual patients.
Reference
1. Platt JF, et al. Liver metastases: Early detection based on abnormal contrast material enhancement at dual-phase helical CT. Radiology 1997;205:49-53.
In patients with breast cancer:
a. the hepatic attenuation ratio at triple-phase helical CT is decreased in those patients who develop liver metastases.
b. the hepatic enhancement ratio at triple-phase helical CT is decreased in those patients who develop liver metastases.
c. liver metastases usually develop if, at triple-phase helical CT, the hepatic enhancement ratio at 30 seconds exceeds 0.4.
d. triple-phase helical CT of the liver cannot be used to reliably predict which patients will develop overt liver metastases.
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