Which types of tumors must be abstracted and assigned a Behavior Code of 3 as of January 1, 2021?

The correct choice is based on the classification of specific tumor types that require a Behavior Code of 3, indicating that they are malignant tumors. Gastro-intestinal stromal tumors (GISTs) and thymomas are included in this category because they exhibit aggressive behavior and have the potential to spread to other parts of the body, necessitating their abstraction and classification as malignant.

GISTs, for instance, are known to be tumors arising from interstitial cells of Cajal or precursor cells in the gastrointestinal tract, often carrying mutations that lead to malignancy. Similarly, thymomas, which arise in the thymus gland, can also be classified as malignant if they demonstrate invasive properties. The coding and abstraction practices must reflect their potential impact on treatment and prognosis, hence the assignment of a Behavior Code of 3 for these specific tumors.

The other choices contain lesions or tumor types that do not meet the criteria for abstraction as malignant. Carcinoma in situ, for instance, while significant, typically receives a different coding focus as its malignancy is confined to its site without invasion. Non-cancerous lesions, benign tumors, and pathological classifications like metastatic or lymphatic tumors do not align with the specific criteria calling for a Behavior Code of 3 as established