[388] Comparison of Clinicopathologic Features, Preoperative Fine Needle Aspiration, and Expression of Immunohistochemical Markers in Thyroid Papillary Microcarcinoma and Thyroid Papillary Carcinoma
F Lin, H Liu, J Shi, P Dorion, K Zhang, PK Pellitteri, C Schuerch. Geisinger Medical Center, Danville, PA
Background: Thyroid papillary microcarcinoma (TPMC) is defined by WHO as thyroid papillary carcinoma (TPC) smaller than 1.0 cm. Some investigators consider TPMC as 
incidental
and clinically insignificant; others believe that TPMC should be regarded as classic papillary carcinoma. In this study, we evaluate the clinicopathologic features, preoperative diagnosis on fine needle aspiration (FNA), and expression of some tumor-associated markers in both TPMC and TPC.
Design: One hundred ninety-three consecutive cases of papillary carcinoma of the thyroid were included and divided into three groups as in Table 1. Immunohistochemical stains for galactin 3, c-Met, S100A4, and S100A6 were performed in 58 cases. The staining intensity and distribution were recorded.
Results: The immunostaining results were diffuse and strong staining for all markers in the majority of cases in G1, G2 and G3. The status of preoperative FNAs and results for G2 and G3 were summarized in Table 2. Seventy-three percents of cases in G2 and 52% cases in G3 received the preoperative diagnosis by FNAs. TPMC accounted for 42% (81/193) of the total cases; and 62% (50/81) of TPMC received the preoperative FNAs.
| Group | Cases | Age # | F:M | F. Variant* | Size (cm) | Metastasis (%) |
| G1 (>1.0cm) | 113 | 46 | 2.3:1 | 28 (25%) | 2.96 | 36 (32%) |
| G2 (0.5 - 1.0cm) | 37 | 51 | 4.3:1 | 11 (30%) | 0.76 | 6 (16%) |
| G3 (<0.5cm) | 44 | 52 | 3.8:1 | 24 (55%) | 0.17 | 0 |
| Tumor size (cm) | Positive on FNA | Suspicious/atypical on FNA | Negative on FNA | FNA not done |
| G2 (0.5-1.0, N = 37) | 14/37 (38%) | 11/37 (30%) | 2/37 (5%) | 10/37 (27%) |
| G3 (<0.5, N=44) | 7/44 (16%) | 9/44 (20%) | 7/44 (16%) | 21/44 (48%) |
Conclusions: These data indicate 1) TPMC expresses similar markers to TPC, including markers associated with unfavorable prognosis; 2) metastasis is present in 16% of TPMC only when a tumor is larger than 0.5 cm; 3) Since TPMC accounts for 42% of the total cases in this study, it should not be considered as
incidental especially when a tumor is larger than 0.5cm. Therefore, we propose that TPMC should be defined as papillary carcinoma smaller than 0.5 cm, and a tumor larger than 0.5 cm should be clinically regarded as classic TPC.Category: Cytopathology
Monday, March 9, 2009 1:00 PM
Platform Session: Section F, Monday Afternoon