Key Background
8
Cytology, Histopathology, And Differential Diagnosis
Recommendation 1
➤ FNA cytology can play an important diagnostic role in the initial
evaluation of ATC, but parallel core biopsy may be necessary for
definitive diagnosis and to obtain sufficient material for molecular
interrogation. (S-L)
Recommendation 2
➤ Every effort should be made to establish a diagnosis via biopsy before
proceeding with surgical resection, as surgical resection may be
inappropriate. (S-L)
Recommendation 3
➤ Routine surgical pathology evaluation of resection specimens should
focus on confirming a definitive diagnosis of ATC, documenting extent
of disease, and defining the presence of any coexisting DTC and/
or other pathologies. The proportion of tumor that represents ATC
should also be documented. (S-L)
Diagnosis
RECIST Response
➤ Response Evaluation Criteria in Solid Tumors (RECIST) are used
to assess objectively the effects of systemic therapy on tumor
dimensions/size (10). After determining the baseline diameters of
index lesions (must be >1 cm for visceral lesions, >1.5 cm short axis
for nodal metastases; only two measured lesions per disease site/
organ allowed, generally the largest) with cross-sectional imaging
(computed tomography [CT], magnetic resonance imaging [MRI]),
follow-up measurements of the same lesions are determined at
defined intervals and compared with baseline as a percentage
of the sum of all index lesions. A complete response (CR) means
disappearance of all lesions; a partial response (PR) is at least a 30%
reduction in the lesional sum, confirmed at least once at a ≥4-week
interval once observed; progressive disease (PD) is a 20% or greater
increase in lesional sum from baseline or nadir; and stable disease
(SD) refers to tumors not reaching criteria for either PR or PD. Of note
is that these criteria require the absence of new locations of disease.
and the absence of growth of any nontarget lesions.
