Tall cell variant cutoff IDs highest-risk papillary thyroid carcinomas

CHICAGO — Tall cell percentages between 30% and 49% appeared associated with higher tumor aggressiveness among patients with papillary thyroid carcinoma, according to study results presented at the Annual Meeting of the American Thyroid Association.

“Patients with papillary thyroid carcinomas with more than 30% tall cell areas appear significantly more invasive. Therefore, the 30% tall cell cutoff can be considered adequate,” Fulvio Basolo, MD, researcher in the department of surgical, medical and molecular pathology and critical area at University of Pisa in Italy, said during a presentation.

Papillary thyroid cancer is the most common subtype of thyroid cancer, and incidence is increasing worldwide.

The particularly aggressive tall cell variant accounts for 1.3% to 13% of all papillary thyroid cancer cases. OS and DFS tend to be about 10% shorter for patients with the tall cell variant compared with those who have classic papillary thyroid carcinoma.

In 2017, WHO defined the tall cell variant as papillary thyroid carcinoma that contains at least 30% tall cells. However, controversy has persisted about the appropriate proportion of tall cells required to diagnose the variant.

Basolo and colleagues sought to clarify the association between tall cell percentage and tumor aggressiveness.

They evaluated 2,834 consecutive patients with a combined 3,133 tumors diagnosed as papillary thyroid carcinoma or tall cell variant between 2000 and 2017.

Investigators revised all cases to the current classification and then divided them into four categories based on tall cell percentages.

The researchers also correlated each group with clinicopathological parameters, including age, sex, invasiveness, multifocality, node metastases, vascular invasion and presence of thyroiditis.

Basolo and colleagues determined 205 tumors (6.5%) had 10% or fewer tall cells; 416 tumors (13.3%) had 11% to 29% tall cells; 495 tumors (15.8%) had 30% to 49% tall cells; and 2,017 tumors (64.4%) had 50% or more tall cells.

Results showed tumors with 30% to 49% tall cells had significantly more extra-thyroidal extension, vascular invasion and node metastases (P < .001). Multifocality appeared more common in papillary thyroid carcinomas with lower percentages of tall cells.

Tumors with 50% or more tall cells were significantly smaller and also more frequently occurred among older patients (P < .0001).

Researchers also evaluated the correlation with BRAF status in a subgroup of 316 patients. The majority (85%) of those patients had BRAF mutations, 13% of patients had TERT promoter mutations and 12% had both BRAF and TERT mutations.

“TERT promotor mutations can predict the risk for recurrence independently of tall cell percentage. Both TERT and BRAF testing can help refine the risk stratification of papillary thyroid cancer,” Basolo said. – by Jennifer Southall

Reference:

Proietti A, et al. Short Call Oral Abstract 7. Presented at: Annual Meeting of the American Thyroid Association; Oct. 30-Nov. 3, 2019; Chicago.

Disclosures: The authors report no relevant financial disclosures.