Diffuse sclerosing variant of papillary thyroid carcinoma: a clinicopathologic and immunophenotypic analysis of 22 cases.

BACKGROUND

The diffuse sclerosing variant of papillary thyroid carcinoma (DSV-PTC) is an uncommon tumor making up about 2% of all papillary thyroid carcinomas. Previous studies have not comprehensively evaluated these tumors in a large series of patients.

DESIGN

Twenty-two cases of DSV-PTC diagnosed between 1970 and 2000 were identified in the files of the AFIP. Histologic and immunohistochemical features were evaluated and patient follow-up was obtained.

RESULTS

The tumors affected 14 females and 8 males, aged 6 to 49 yr (mean, 18 yr), with males presenting at a mean older age than females (24 vs 14 yr). Symptoms included an enlarging mass in the thyroid, present for a mean of 9.5 mo. While a dominant tumor was identified in a single lobe, bilateral disease was common (n = 16). The dominant mass ranged in size from 1.7 to 5.8 cm in diameter (mean, 3.8 cm). Histologically, all cases demonstrated a papillary carcinoma (conventional, solid, or follicular pattern) diffusely involving the gland. Extrathyroidal extension, lymphocytic thyroiditis, squamous metaplasia, increased fibrosis/sclerosis, and psammoma bodies were present to a variable degree. Both the papillary carcinoma and squamous metaplasia cells were strongly immunoreactive with CK19, thyroglobulin, and TTF-1. An increased number of S-100 protein immunoreactive dendritic cells were recognized. p53 was increased (>15%) in the tumor cells in 12 patients, while Ki-67 was increased in the tumor cells in two patients. Perithyroidal and cervical lymph node metastasis occurred in 18 (82%) patients. All metastases demonstrated histologic features similar to the primary. Complete resection (thyroidectomy in 18 patients) with lymph node dissection, yielded a 95% 5-yr survival without evidence of disease. One patient died of disease after a malignant transformation of the squamous metaplasia into squamous cell carcinoma.

CONCLUSIONS

The recognition of DSV-PTC can be made with the following features: classic to solid foci of PTC, lymphocytic thyroiditis, squamous metaplasia, increased fibrosis, and innumerable psammoma bodies. DSV-PTC is more biologically aggressive than conventional PTC, but the patients' survival is not significantly different. This diagnosis should lead the clinician to aggressively manage these patients (thyroidectomy and lymph node dissection) in an effort to achieve an excellent long-term clinical outcome.