Undifferentiated Sarcomatoid Carcinoma of the Pancreas: From Histology and Molecular Pathology to Precision Oncology

Undifferentiated sarcomatoid carcinoma of the pancreas-a single-institution experience with 23 cases

BACKGROUND

The clinical course and surgical outcomes of undifferentiated sarcomatoid carcinoma of the pancreas (USCP) remain poorly characterized owing to its rarity. This study aimed to describe the histology, clinicopathologic features, perioperative outcomes, and overall survival (OS) of 23 resected USCP patients.

METHODS

We retrospectively described the histology, clinicopathologic features, perioperative outcomes and OS of patients who underwent pancreatectomy with a final diagnosis of USCP in a single institution.

RESULTS

A total of 23 patients were included in this study. Twelve patients were male, the median age at diagnosis was 61.5 ± 13.0 years (range: 35-89). Patients with USCP had no specific symptoms and characteristic imaging findings. The R0 resection was achieved in 21 cases. The En bloc resection and reconstruction of mesenteric-portal axis was undertaken in 9 patients. There were no deaths attributed to perioperative complications in this study. The intraoperative tumor-draining lymph nodes (TDLNs) dissection was undergone in 14 patients. The 1-, 3- and 5-year survival rates were 43.5%, 4.8% and 4.8% in the whole study, the median survival was 9.0 months. Only 1 patient had survived more than 5 years and was still alive at last follow-up. The presence of distant metastasis (p = 0.004) and the presence of pathologically confirmed mesenteric-portal axis invasion (p = 0.007) was independently associated with poor OS.

CONCLUSIONS

USCP was a rare subgroup of pancreatic malignancies with a bleak prognosis. To make a diagnose of USCP by imaging was quite difficult because of the absence of specific manifestations. Accurate diagnosis depended on pathological biopsy, and the IHC profile of USCP was mainly characterized by co-expression of epithelial and mesenchymal markers. A large proportion of patients have an early demise, especially for patients with distant metastasis and pathologically confirmed mesenteric-portal axis invasion. Long-term survival after radical resection of USCPs remains rare.

Genomic characterization of undifferentiated sarcomatoid carcinoma of the pancreas

Undifferentiated sarcomatoid carcinoma (USC) of the pancreas is a rare but especially aggressive variant of pancreatic ductal adenocarcinoma (PDAC), composed of at least 80% of sarcomatoid cells. This study aimed to elucidate its clinicopathological and molecular features. The study cohort included 10 patients with pancreatic USC. Clinicopathological parameters were determined for each patient. The molecular profile was investigated using next-generation sequencing (NGS). Histologically, all tumors were hypercellular neoplasms with spindle-shaped or sarcomatoid cells. All patients showed vascular and perineural invasion. Most patients had a poor prognosis. NGS showed important similarities with conventional PDAC, including frequent alterations in the classic PDAC drivers, KRAS (100% of cases), TP53 (90%), and CDKN2A (60%). There were also some important distinctions from conventional PDAC: 1) SMAD4, a typical PDAC driver gene, was mutated in only one case (10%); 2) Another distinctive molecular feature was the recurrent KRAS amplification (30% of cases), which is very rare in conventional PDAC. It has been previously reported in another subtype of pancreatic undifferentiated carcinoma, the rhabdoid variant, and may be a key event leading to the acquisition of an undifferentiated phenotype in a subgroup of cases; 3) Lastly, in two different cases, we detected two potentially actionable targets, not belonging to the typical PDAC molecular landscape, such as MCL1 amplification and POLQ mutation. Our study sheds light on this rare tumor type, which shows aggressive biological behavior and few druggable alterations. The most distinctive molecular features of pancreatic USC are the paucity of SMAD4 alterations and recurrent KRAS amplification.