MRI-Invisible Prostate Tumors: What Is the Real Risk?

Prostate cancer diagnosis and follow-up increasingly rely on magnetic resonance imaging (MRI), yet this technique sometimes encounters a surprising phenomenon:

Lesions identified in a pathology report after biopsy are sometimes not visible on MRI. To radiologists, the prostate tissue appears completely normal.

Why are these lesions invisible on MRI, and does this pose a danger to patients?

MRI-Invisible Lesions: A Cause for Concern?

Some experts argue that these lesions are usually harmless. In their view, a cancer that is not visible on MRI is not clinically significant. The prevailing view is that MRI-invisible cancers are mostly insignificant and do not require systematic biopsy .

These experts compare MRI-invisible lesions to cancers with a Gleason score of 6 or below , namely low-risk prostate cancer. Such cancers generally progress slowly and carry no risk of spread or death. Among patients under active surveillance, those with MRI-invisible cancers have a much more favorable disease course than those with visible cancers.

Opposing Views: Is Every Invisible Lesion Harmless?

However, some experts argue that MRI-invisible lesions are not entirely harmless. Lesions visible on MRI generally indicate more aggressive tumors, but this generalization may not apply to every individual.

According to research, MRI scans may produce false-negative results in 10-20% of patients with clinically significant prostate cancer.

In one analysis, among men without a suspicious lesion on MRI, 16% were diagnosed with clinically significant prostate cancer on biopsy. In another analysis of MRI-invisible prostate cancers, 35% were found to be clinically significant.

Negative MRI Findings: Misleading or Reassuring?

Some studies confirm that negative MRI findings indicate a low risk of developing clinically significant cancer. JAMA Oncology published a study in which only 3% of 233 men with negative MRI findings were diagnosed with clinically significant prostate cancer after 3 years of follow-up.

Why Does MRI Fail to Detect Some Tumors?

MRI may miss some cancers for two main reasons:

1. Small, aggressive tumors: The tumor may be too small to be detected by MRI.

2. An appearance similar to surrounding tissue: Some low-grade cancers may look similar to normal prostate tissue and therefore go unnoticed.

The experience of the radiologist interpreting the MRI scans may also affect the results.

Genetic Profiles and MRI Visibility

The genetic profiles of MRI-visible and MRI-invisible prostate cancers differ. Gene expression in visible disease has generally been associated with more aggressive tumors.

In one study, PHYHD1, CENPF, ALDH2 and GDF15 gene expression was found to be more common in MRI-visible tumors, and these genes were associated with a less favorable disease course.

What Should Be Done After a Negative MRI?

Should a patient with elevated PSA levels but a normal MRI result undergo biopsy?

Biopsy is generally unnecessary in these patients, but they should be monitored with periodic MRI follow-up.

On December 12, 2024, JAMA Oncology published a study in which 86% of men with negative MRI findings avoided biopsy within 3 years, and clinically significant prostate cancer was detected in only 4% during this period.

How Should the Need for Biopsy Be Determined?

When biopsy is necessary, it is important to systematically sample areas outside the targeted region as well. These additional tissue samples add no more than 1-2 minutes to the procedure and do not greatly increase its risks.

A biopsy should be performed if imaging shows progression. However, avoiding routine biopsy may protect thousands of patients from biopsy-related complications such as infection.

Conclusion

MRI appearance may be a powerful predictor of risk when assessing the aggressiveness of prostate cancer. However, individual risk assessment is important for every patient. PSA levels, MRI findings, and the patient's overall clinical profile should be evaluated together to determine the need for biopsy.