α-Smooth Muscle Actin Expression in Relation to Invasive Histopathological Features of Papillary Thyroid Carcinoma

Papillary thyroid carcinoma (PTC) generally has a favourable prognosis, but some tumours show invasive histopathological features associated with more aggressive behaviour. Alpha-smooth muscle actin (α-SMA), a marker of activated cancer-associated fibroblasts, has been linked to postoperative recurrence in PTC in a companion analysis of this cohort (unpublished data), but its relationship with conventional invasive features is unclear. This retrospective study included 49 patients with PTC treated at a tertiary referral hospital in Surabaya, Indonesia. Stromal α-SMA expression was assessed immunohistochemically and quantified using the H-score. Tumour size category, multifocality, extrathyroidal extension, lymphovascular invasion, perineural invasion, lymph node metastasis and morphological subtype were extracted from archived histopathology reports. Groups were compared using the Mann-Whitney U and Kruskal-Wallis tests and Spearman correlation, using all patients with available data for each variable. Stromal α-SMA H-score did not differ significantly according to multifocality (p=0.852), extrathyroidal extension (p=0.630) or lymphovascular invasion (p=0.854), or across tumour size categories (p=0.422), and subtype was not significantly associated with H-score (p=0.113). Lymph node metastasis (2 node-negative patients) and perineural invasion (1 positive patient) were described only. Because subgroups were small and statistical power was low, a Type II error cannot be excluded. These findings suggest that stromal α-SMA expression is not simply a surrogate of conventional anatomical invasiveness and may reflect a distinct axis of tumour-stroma interaction that should be confirmed in larger multicentre cohorts.