Long-term disease recurrence in the adipose tissue and striated muscles of a minimally invasive papillary thyroid carcinoma

Differentiated thyroid carcinomas (DTCs), particularly papillary thyroid carcinomas (PTCs), usually have an indolent behavior, however, 10–20% of the patients may develop recurrent disease, usually in the central compartment lymph nodes, following surgery. There are several histological features associated with more frequent recurrences: the histopathologic variants of PTCs, the presence of vascular invasion or lymph node metastases, and the presence of extrathyroidal extension (ETE) are associated with loco-regional recurrences and distant metastases. The extrathyroid extension occurs in up to 30% of DTCs, although extensive ETE is observed in only 5% and may be associated with an increased risk of recurrence. Its role in tumor mortality risk is more debated. In the seventh edition of its Cancer Staging Manual, the American Joint Committee on Cancer (AJCC) defines the minimum extra-thyroid extension (mETE) as the involvement of the peri-thyroid muscles, fascia or soft tissues, visible only microscopically. The eighth edition of the AJCC Cancer Staging Manual has changed the criteria so that only grossly evident (macroscopic) ETE involving strap muscles (not microscopic ETE involving perithyroidal soft tissue) affects tumor staging. The American Thyroid Association (ATA) recommends the use of the AJCC TNM staging to evaluate thyroid cancer mortality risk. On the contrary, the ATA risk stratification system is used to estimate structural recurrence risk and it still includes minimal extrathyroidal extension as a prognostic feature. We report the case of a massive metastasis in adipose and striated muscle tissues of the neck, in a patient with papillary thyroid carcinoma with minimal ETE, 12 years after the primary treatment with excellent response.