Tall cell papillary thyroid carcinoma (TC-PTC) is considered adverse histology. However, previous studies are confounded by inconsistent criteria and strong associations with other adverse features. It is therefore still unclear if TC-PTC represents an independent prognostic factor in multivariate analysis and, if it does, what criteria should be employed for the diagnosis. We retrospectively reviewed 487 PTCs from our institution (where we have historically avoided the prospective diagnosis of TC-PTC) for both the height of tall cells (that is if the cells were two, or three, times as tall as wide) and the percentage of tall cells. On univariate analysis, there was significantly better disease free survival (DFS) in PTCs with no significant tall cell component (< 30%) compared to PTCs with cells two times tall as wide (p = 0.005). The proportion of tall cells (30–50% and > 50%) was significantly associated with DFS (p = 0.012). In a multivariate model including age, size, vascular space invasion, and lymph node metastasis, the current WHO tall cell criteria, met by 7.8% of PTCs, lacked statistical significance for DFS (p = 0.519). However, in the subset of tumours otherwise similar to the American Thyroid Association (ATA) guidelines low-risk category, WHO TC-PTC demonstrated a highly significant reduction in DFS (p = 0.004). In contrast, in intermediate to high-risk tumours, TC-PTC by WHO criteria lacked statistical significance (p = 0.384). We conclude that it may be simplistic to think of tall cell features as being present or absent, as both the height of the cells (two times versus three times) and the percentage of cells that are tall have different clinical significances in different contexts. Most importantly, the primary clinical significance of TC-PTC is restricted to PTCs that are otherwise low risk by ATA guidelines.

高细胞甲状腺乳头状癌（TC-PTC）被认为是不良组织学。然而，之前的研究因标准不一致以及与其他不良特征的强烈关联而令人困惑。因此，目前尚不清楚 TC-PTC 是否代表多变量分析中的独立预后因素，如果是，则应采用什么标准进行诊断。我们回顾性审查了我们机构（我们历来避免前瞻性诊断 TC-PTC）的 487 个 PTC，了解高细胞的高度（即细胞高是宽的两倍或三倍）和百分比高的细胞。在单变量分析中，与具有两倍高细胞宽度的 PTC 相比，不具有显着高细胞成分 (< 30%) 的 PTC 的无病生存 (DFS) 显着更高 (p = 0.005 )  。高细胞的比例（30-50% 和 > 50%）与 DFS 显着相关（p  = 0.012）。在包括年龄、大小、血管间隙侵犯和淋巴结转移的多变量模型中，7.8% 的 PTC 符合当前的 WHO 高细胞标准，但 DFS 缺乏统计学意义（p = 0.519 ）  。然而，在与美国甲状腺协会 (ATA) 指南低风险类别类似的肿瘤子集中，WHO TC-PTC 表现出 DFS 显着降低 ( p  = 0.004)。相比之下，在中危至高危肿瘤中，根据 WHO 标准，TC-PTC 缺乏统计学意义 ( p  = 0.384)。我们的结论是，认为存在或不存在高细胞特征可能过于简单化，因为细胞的高度（两倍与三倍）和高细胞的百分比在不同情况下具有不同的临床意义。最重要的是，TC-PTC 的主要临床意义仅限于 ATA 指南中风险较低的 PTC。