What is the characteristic feature of anaplastic thyroid cancer?

Anaplastic thyroid cancer is known for its aggressive behavior and rapid clinical progression. One of the hallmark characteristics of this type of cancer is the presence of a rapidly enlarging neck mass. This feature distinguishes it from well-differentiated thyroid cancers, which typically grow more slowly and may not exhibit significant changes in size over a short period. The rapid enlargement correlates with the aggressive nature of anaplastic thyroid cancer, which often results in invasion of surrounding structures and metastasis.

While other types of thyroid cancer may present with painless nodules or secretions like calcitonin, these traits are not characteristic of anaplastic cancer. Additionally, anaplastic thyroid cancer generally carries a poor prognosis, contrasting with the idea of a "good prognosis." This further underscores the need for immediate diagnosis and intervention when a rapidly enlarging neck mass is observed in patients, as it may indicate the presence of this aggressive form of thyroid malignancy.