Incidental thyroid cancer is a term applied to very small, unsuspected papillary cancer identifiedincidentally on pathologic examination of thyroid tissue removed for benign disease. Incidental thyroid cancer is also known as micro papillary thyroid cancer. Depending on the source, micro papillary cancer may be broadly defined as papillary cancer of the thyroid <5 mm in greatest dimension.Our discussion on this page is an effort to help our patients understand the implication of this finding.
Autopsy studies tell us that 3-4% of the adult population harbors micro papillary carcinoma of the thyroid without apparent ill effect. Approximately 1 in 15 patients who undergo thyroidectomy for benign disease are found to have an incidental 1-2 mm focus of thyroid cancer on careful pathologic examination. Based on extensive clinical experience the vast majority of these incidental carcinomas are not thought to be clinically relevant and cause no discernible harm to the patient.
Pathologist don’t consider this entity to be different from larger tumors (> 1 cm) but surgeons and other clinicians do. Papillary cancer greater than or equal to 1 cm has a real possibility of spread to surrounding tissue, lymph nodes and distant metastasis. As we have discussed on other pages, this type of thyroid cancer is treated with total thyroidectomy usually accompanied by a level 6 node dissection. Micro papillary thyroid cancer (<5 mm) rarely metastasize (<1% risk). Therefore the benefit of any further therapy is miniscule and does not justify the risks involved. Generally, no further specific therapy is recommended.
When an incidental micro papillary cancer is found on the pathology report, no further surgery or radioactive iodine therapy or work-up is required. If a simple lobectomy has been performed then a completion thyroidectomy is ,generally, not required. If a total thyroidectomy has been performed return to the operating room for a node dissection is not appropriate. Radioactive iodine ablation is not indicated. There are no high quality scientific studies to support an aggressive approach to this clinical problem.
Whether suppressive therapy following this diagnosis is helpful is unknown. Given the lack of evidence for benefit and the potential downside of long term suppressive therapy it is infrequently recommended.
The above generalization are guidelines only. There are situations when micro papillary cancer should be more aggressively treated, a example would be if an incidental papillary cancer showed an aggressive cell-type such a tall-cell cancer. Or if the patient had a history of significant head and neck radiation or multiple foci of cancer. DNA analysis of these tumors (e.g. BRAF mutations) may be able to help us decide when to be aggressive with small thyroid cancers but more study is needed.
In conclusion, incidentally noted micro papillary cancer found on pathologic inspection of thyroid tissue removed for benign disease does not require further treatment. Each case should be considered individually. All patients should be followed yearly with careful physical exam. Whether ultrasound screening during follow-up is helpful or cost effective is unknown but seems a reasonable approach to consider.