Prognostic Nomogram for Retroperitoneal Sarcoma Validated in Large Cohort

A new study validated a prognostic nomogram for retroperitoneal sarcoma (RPS) using a large, external cohort. The nomogram incorporates six variables, and provided strong concordance with observed disease-free survival (DFS) and overall survival (OS).

RPS account for about 15% of all soft-tissue sarcomas, and their unique characteristics make traditional staging difficult, according to study authors led by Chandrajit P. Raut, MD, of Brigham and Women’s Hospital in Boston. A multi-institutional nomogram was developed previously based on a 523-patient cohort who underwent surgical resection for RPS between 1999 and 2009.

The nomogram included six clinical characteristics and variables: age at the time of diagnosis; tumor size; FNCLCC tumor grade; histologic subtype; multifocality at the time of initial presentation; and extent of surgical resection. Because the American Joint Committee on Cancer (AJCC) is considering including this tool in its forthcoming revised staging system, the study authors decided to validate it in an external cohort of 631 RPS patients who underwent surgery at one of six centers. The results were published online ahead of print in Cancer.

The 7-year DFS rate in the validation cohort was 38.4%, and the 7-year OS rate was 58%. This was similar to the development cohort’s outcomes, at 35.7% and 50.5%, respectively. All six of the nomogram’s included variables were found to be independently prognostic.

The researchers used a Harrell C-statistic to measure the nomogram’s discriminative ability. For DFS, the result was 0.69, while for OS it was 0.73. These were very similar to the concordance rates found in the development cohort (0.71 and 0.74, respectively).

“Correlation between observed and nomogram-predicted DFS and OS rates suggest good calibration of the multi-institutional RPS nomogram in a larger, independent validation cohort,” the authors wrote. “External validation of the…nomogram established its broad applicability in predicting outcomes in patients with primary RPS who were treated at experienced centers, and supports its inclusion in the 8^th edition of the AJCC classification.”

Study Details

The median age in the validation cohort was 59 years, and the median tumor size was 21 cm. There were similar numbers of patients with FNCLCC grade 1 (32.7%), 2 (39.8%), and 3 (27.5%) tumors.

The most common histologic subtype was dedifferentiated liposarcoma (36.6%), followed by well-differentiated liposarcoma (25%), leiomyosarcoma (21.7%), and other subtypes. Almost all patients (94.8%) had a complete resection. Most patients (91%) did not receive chemotherapy or radiotherapy (68.3%).