Case 75
- Wangpan Shi
- Mar 16
- 1 min read
A 77-year-old female with a large appendix mass.
What's your diagnosis?
A: Poorly differentiated carcinoma
B: Invasive lobular carcinoma
C: Well differentiated neuroendocrine tumor
D: Goblet cell adenocarcinoma
Answer
The correct answer is C. It's a well-differentiated neuroendocrine tumor, grade 1. Immunostains performed at the outside institution are available for review. Tumor cells are diffusely positive for CD56, synaptophysin, and chromogranin, and they are negative for CK7 and CK20. Ki-67 shows a proliferation index of less than 3%. Findings are consistent with a well-differentiated neuroendocrine tumor, grade 1.
Feature | EC-cell NET | L-cell NET | Tubular NET (Rare) |
Cell Type | Uniform polygonal tumour cells | L-cells producing GLP-1 & proglucagon peptides | Must be distinguished from adenocarcinoma & goblet cell adenocarcinoma |
Growth Pattern | Large nests with peripheral palisading, glandular formations | Trabecular or glandular growth pattern | Tubular structure |
Location | Deep muscular wall & subserosa | Similar to rectal L-cell NETs | N/A |
Stromal Response | Fibrotic stromal response in most cases | N/A | N/A |
Necrosis | Uncommon | N/A | N/A |
Mitoses | Infrequent to absent | N/A | N/A |
Mesappendiceal Infiltration | About one-third of cases; 50–82% infiltrate <3 mm | N/A | N/A |
Grading | Mostly G1 (86–91%) or G2 (9–14%) | Mostly G1 (86–91%) or G2 (9–14%) | N/A |
Diagnostic Consideration | Stromal retraction artefact should not be misinterpreted as vascular invasion | Not required to specify in pathology reports | N/A |
Prognostic Value & Treatment Impact | No prognostic value or treatment consequences | No prognostic value or treatment consequences | N/A |
Case credit: UCSD Pathology
Author: Wangpan Jackson Shi, MD
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