Positive RET Staining Associated with Low Risk of Recurrence, Death in Thyroid Cancer

Positive RET staining by immunohistochemistry was associated with a low risk of recurrence and death from papillary thyroid cancer, according to a new exploratory analysis published inCancer Medicinethat examined a cohort of 231 patients with long-term follow-up at a single institution.¹

“It is possible that genetic, transcriptional, or post‐translational regulation of factors along [the RET onco-genetic] pathway could have similar downstream effects even in the absence of upstream genetic activation,” the authors, led by Alexander J. Lin, MD, PhD, of Washington University in St Louis, wrote. “Therefore, we sought to characterize the molecular expression at the protein level of 5 factors along the BRAF and RAS pathways… [and] to identify molecular signatures that may be associated with clinical outcomes.”

The authors constructed a tissue microarray using analyzable tumor specimens collected from patients who underwent partial or complete thyroidectomy at Washington University between 1973 and 2009. Of the 231 patients with interpretable immunohistochemistry stains, the mean follow-up was 10.1 years (range, 0.1‐40 years).

When the authors stratified the samples for risk according to the 2015 American Thyroid Association (ATA) criteria, they found that nearly half the cohort had high-risk disease (42%, n = 96), while 32% of patients (n = 74) had intermediate-risk disease. About a quarter of the samples were stratified as low risk (26%, n = 61).

Of the 231 patients, 212 were adults and 19 were ≤21 years of age. The mean age for adult patients was 47 years (range 23‐82 years) compared to 16 years (range 6‐21 years) for pediatric patients. ATA risk groups were represented equally between adult and pediatric patients, but tumor size and nodal stage were significantly higher in pediatric patients. Nearly all the patients received adjuvant I-131 and about half underwent cervical lymph node dissection.

The authors foundBRAFV600E mutation in 74% of the samples (170 of 231 patients). The mutation’s incidence was similar in adult and pediatric patients. The mutation was most prevalent among samples from the ATA high-risk group (82%), followed by the intermediate-risk group at 73% and then the low-risk group at 61%.

Analysis revealed thatBRAFV600E mutation was associated with clinical stage T3‐4 (odds ratio [OR], 2.2; 95% CI, 1.2‐4.2). Capsular invasion (OR, 2.0; 95% CI, 1.1‐3.6), and soft tissue invasion (OR, 2.3; 95% CI, 1.2‐4.4) also showed an association.

Two blinded investigators tested the tissue micro-array for immunohistochemistry and found positive results as follows: RET, 61%; mitogen‐activated protein kinase/extracellular signal‐related kinase (MAPK/ERK), 14%; peroxisome proliferator-activated receptors - gamma (PPARy), 27%; and phospho-related AKT (pAKT) 39%.

AlthoughBRAFV600E mutation was not associated with most molecular markers, the investigators did find an inverse link to MAPK (dpERK) immunohistochemistry intensity (OR, 0.43; 95% CI, 0.19‐0.97).

When Lin et al compared these results to tumor and patient characteristics and outcomes, they found that positive RET staining was associated with a lower risk of recurrence (HR, 0.46; 95% CI, 0.22‐0.96). No other molecular biomarkers were independent predictors of recurrence on univariable analysis.

In looking at recurrence, the authors found that 34 of 231 patients (14.7%) experienced recurrence during a mean of 10 years of follow-up. The neck lymph nodes were by far the most common site, affecting 23 patients (67%). Rates of recurrence were 25% for the ATA high-risk group, 10% for the intermediate-risk group, and 5% for the low-risk group. The freedom from recurrence (FFR) rate 74% in the high-risk group, compared with 95% of the pooled low- and intermediate-risk groups.

Nine patients (3.9%) eventually died of thyroid cancer. Stratified by risk group, the death rates were 8.3% among high-risk patients, 1.4% among intermediate-risk patients, and 0% among low-risk patients. No molecular marker was independently associated with cancer-specific death, although older age, higher T stage, metastatic disease, vascular and soft-tissue invasion, and positive margins all had significant associations.

Lin et al performed an exploratory analysis to attempt to identify a molecular signature that independently predicted a high risk of recurrence. Based on their model, they identified a molecular low-risk group consisting of patients whose tumors were positive for RET staining (10% recurrence risk) and negative for RET, pAKT, and MAPK (dpERK) (16% recurrence risk). The molecular high-risk group was composed of patients whose samples had negative RET staining and either positive pAKT or MAPK (dpERK) staining (42% recurrence risk).

They estimated the molecular high-risk group had a significantly lower 10‐year FFR versus the low-risk group (57% vs 90%). They also found that the presence ofBRAFV600E mutation was not associated with recurrence risk in either group.

“The molecular high‐risk profile was found in 9%, 14%, and 13% of ATA low‐, intermediate‐, and high‐risk groups, respectively (P= 0.77), suggesting the prognostic information gained from each of the two risk stratifications is unique,” Lin et al wrote.

Their multivariable model found that recurrence was independently associated with both ATA high-risk (HR, 2.8; 95% CI, 1.3‐6.0;P= 0.008) and the molecular high‐risk traits (HR, 5.4; 95% CI, 2.5‐12;P<.001).

They also found that cancer‐specific death was independently associated with both ATA high risk (HR, 9.3; 95% CI, 1.1‐76;P= 0.04) and the molecular high‐risk signature (HR, 4.3; 95% CI, 1.0‐18;P= .05).

&ldquo;The molecular risk score also assigned risk of recurrence independent of classic pathologic findings, suggesting molecular subtypes of cPTCs may explain some of the heterogeneity seen in outcomes based on the 2015 ATA risk classification system,&rdquo; Lin et al wrote. &ldquo;Immunohistochemistry analysis of molecular biomarkers may assist clinicians in further stratifying risk of recurrence when combined with the current ATA risk classifications.&rdquo;

Reference:

Lin AJ, Samson P, DeWees T, et al. A molecular approach combined with American Thyroid Association classification better stratifies recurrence risk of classic histology papillary thyroid cancer.Cancer Med.DOI: 10.1002/cam4.1857.