An inconclusive biopsy result leaves a patient uncertain about their health status. A biopsy removes a small tissue sample from a suspicious area for examination by a pathologist to determine if the cells are cancerous. When results are reported as “inconclusive” or “indeterminate,” the pathologist could not provide a definitive benign or malignant diagnosis. This ambiguity requires further investigation rather than simple dismissal.
Decoding the Term “Inconclusive”
The general term “inconclusive” covers several distinct medical classifications that carry different implications for follow-up care. One category is “Non-Diagnostic” or “Inadequate,” which means the sample was insufficient for proper analysis. This technical failure occurs when the tissue collected is too small, contains too few cells, or missed the actual lesion, preventing the pathologist from making a judgment.
An “Indeterminate” result means the sample was adequate, but the cellular features are ambiguous, placing the finding in a gray zone. “Atypical” findings are common within this category, meaning the cells show abnormal features but lack the full criteria to be classified as cancer. For instance, in thyroid pathology, this can be termed Atypia of Undetermined Significance.
Technical Reasons Why Biopsies Are Indeterminate
The inability to get a clear diagnosis often stems from limitations in the biopsy process. The most common technical issue is an insufficient tissue sample, where the needle only collects a minimal number of cells. This lack of material prevents the pathologist from conducting necessary diagnostic tests or viewing enough cells to establish a clear pattern.
Poor sample quality is another factor, such as when the tissue is crushed or smeared during collection or processing, distorting the cell architecture. Location difficulty can also lead to an indeterminate result, particularly when a lesion is small, deeply situated, or near sensitive structures. Furthermore, if the suspicious area exhibits lesion heterogeneity, the small sample may only capture normal tissue or benign areas mixed within a larger lesion, leading to a misleadingly benign or non-diagnostic result.
Interpreting Risk: When Inconclusive Results Require Concern
An inconclusive diagnosis suggests the probability of malignancy remains elevated compared to a completely benign finding. The risk of cancer following an indeterminate result is highly dependent on the specific findings and the organ involved. A significant percentage of lesions initially classified as inconclusive are later confirmed as malignant upon surgical removal or repeat testing.
Risk is formally stratified based on the cellular features observed, with atypia carrying a higher risk of malignancy than a non-diagnostic result. In thyroid nodules, for instance, Atypia of Undetermined Significance (Bethesda category III) suggests a cancer risk ranging from 10 to over 30%. In contrast, a diagnosis of Suspicious for Malignancy (Bethesda category V) may suggest a risk as high as 60 to 80%.
Next Steps After an Indeterminate Diagnosis
A definitive management plan following an indeterminate result should be discussed with a specialist, such as an oncologist or surgical expert. One common course of action is a repeat biopsy, often performed with better image guidance or a different technique. This aims to ensure a high-quality sample is obtained and move the diagnosis into a clear benign or malignant category.
Advanced imaging, such as an MRI or PET scan, may be ordered to better characterize the lesion’s size, shape, and metabolic activity, providing additional data for risk assessment. Molecular testing can also be performed on the existing sample to look for specific genetic mutations associated with malignancy. A negative molecular test result often provides confidence that the lesion is benign, potentially allowing the patient to avoid surgery.
For findings deemed low-risk based on the full clinical picture, active surveillance may be recommended. This involves scheduled follow-up imaging to monitor the lesion for any changes in size or appearance over time. For high-risk indeterminate lesions, surgical removal of the mass may be necessary to establish a final diagnosis.