A limited panel of INSM1 and LEF1 immunostains accurately distinguishes between pancreatic neuroendocrine tumor and solid pseudopapillary neoplasm

Application of LEF-1 immunohistochemical staining in the diagnosis of solid pseudopapillary neoplasm of the pancreas

INTRODUCTION

Solid pseudopapillary neoplasm (SPN) is a tumor of young females with gain-of-function mutation in catenin beta 1 gene involved in Wnt signal transduction pathway. Beta-catenin immunohistochemistry (IHC) is used to diagnose SPN. Lymphoid enhancer-binding factor 1 (LEF-1) has been recognized in the transactivation of Wnt pathway. We aim to study LEF-1 IHC in SPN and other pancreatic tumors and compare it with beta-catenin IHC.

METHODS

We retrieved cases of SPN, pancreatic neuroendocrine tumor (PanNET), serous cystadenoma (SCA), ductal adenocarcinoma (PDAC) and acinar cell carcinoma (ACC) from 2011 to 2023. Formalin-fixed, paraffin-embedded blocks with adequate tumor were cut and stained with beta-catenin (B-Catenin-1 clone) and LEF-1 (EP310 clone) IHC. Cases were reviewed by two pathologists independently. Nuclear staining with LEF-1 and beta-catenin was considered as positive.

RESULTS

Our cohort consisted of 111 cases [SPN = 59 (42 resections, 11 FNA, 6 biopsies), PDAC = 24, PanNET = 22, SCA = 5, ACC = 1]. For SPN cases male to female ratio was1:8. Age ranged from 9 to 81 years (average: 32 years). Pancreatic tail was the most common location (47 %) followed by head (28 %), body (19 %) and neck (6 %). Tumor size ranged from 1.0 to 12.2 cm (average: 5 cm). Among the SPN cases 57/59 demonstrated strong nuclear LEF-1 staining. 2/49 cases were negative for LEF-1 (both pathologist in agreement). All SPN tumors demonstrated nuclear staining with beta-catenin. Among the non-SPN tumors, beta-catenin showed nuclear staining in 2/52 cases (2 PDAC). The remaining 50 cases were negative for nuclear beta-catenin and demonstrated variable staining pattern with interpretation variability between the two pathologists. The sensitivity and specificity for LEF-1 were 97 % and 100 %, respectively, while for beta-catenin, they were 100 % and 96 % respectively.

CONCLUSION

Crisp nuclear staining of LEF-1 without background staining makes diagnostic interpretation relatively easy and accurate compared to beta-catenin IHC. This is further helpful for small biopsy samples to help differentiate SPN from mimickers such as PanNET. None of the non-SPN cases displayed nuclear LEF-1 rendering it a valuable adjunct to beta-catenin in the diagnostic evaluation of SPN.

Comparison of INSM1 immunostaining with established neuroendocrine markers synaptophysin and chromogranin A in over 14,000 neuroendocrine and non-neuroendocrine tumors

INSM1 is a transcription factor protein which is increasingly used as an immunohistochemical marker for neuroendocrine differentiation. To determine the prevalence of INSM1 expression in tumors and its expression pattern in normal tissues, tissue microarrays containing 14,908 samples from 117 different tumor types/subtypes as well as 76 different normal tissues were analyzed by immunohistochemistry. INSM1 was positive in 89.2% of 471 neuroendocrine neoplasms (NEN) and in 3.5% of 11,815 non-neuroendocrine neoplasms that were successfully analyzed. At least an occasional weak INSM1 positivity was observed in 59 different non-neuroendocrine tumor entities, of which 15 entities contained at least one case with strong INSM1 staining. A comparison with synaptophysin and chromogranin A staining revealed that in NEN, synaptophysin showed the highest sensitivity (93.3%), followed by INSM1 (89.2%) and chromogranin A (87.5%). In neuroendocrine carcinomas (NEC), sensitivity was highest for INSM1 (88.0%), followed by synaptophysin (86.5%) and chromogranin A (66.4%). If INSM1 was used as an additional marker, the sensitivity for detecting neuroendocrine differentiation in NEN increased from 96.6% (synaptophysin and chromogranin A) to 97.2% (synaptophysin, chromogranin A and INSM1). Our study shows that INSM1 is a useful additional marker for neuroendocrine differentiation with high sensitivity, particularly in NEC.

Solid Pseudopapillary Neoplasm of the Pancreas: A Clinicopathological Study of 12 Cases With Emphasis on Diagnostic Pitfalls

INTRODUCTION

Solid pseudopapillary neoplasm of the pancreas (SPNP) is a rare primary neoplasm with distinct clinicopathological features. The tumor most commonly occurs in younger (premenopausal) women and is typified by low malignant potential and an excellent overall prognosis.

METHODS

A retrospective search over 20 years at two referral tertiary care institutions (King Faisal Hospital and Research Center and King Abdulaziz University Hospital, Jeddah, Kingdom of Saudi Arabia) revealed 12 female patients diagnosed with SPNPs. The reslts of ancillary studies performed at the time of diagnosis were also reviewed and placed in the context of current recommendations.

RESULTS

The clinical and pathological findings were reviewed. All patients were females, aged 18 to 30 years. Eight patients presented with abdominal pain, of which two experienced significant weight loss, and four presented with abdominal mass/discomfort. The tumor size ranged from 1.5 and 15 cm. Two cases were initially diagnosed as neuroendocrine tumors (NETs). One of the cases presented as a multifocal disease. All patients were treated surgically with a follow-up period between one and 11 years. Only one patient presented with peritoneal metastasis after seven years of follow-up, but generally, all are doing well.

CONCLUSIONS

We have analyzed 12 SPNP cases in our population over 20 years (2001-2021) in this study. In brief, SPNP is a low-grade malignant potential tumor. Even though SPNP is a recognized entity, diagnostic challenges can arise particularly in the setting of limited sampling. Pathologists must be aware of the classic morphological features of SPNP and the characteristic profile of immunohistochemistry and be able to differentiate SPNP from other mimickers, especially well-differentiated NETs of the pancreas, and ultimately to avoid misdiagnosis and unnecessary oncologic treatment. Adequate surgical resection with negative margins is associated with an excellent outcome.