Case 13 Dermatopathology

1. Case 13Dermatopathology Douglas R. Fullen, M.D. Associate Professor of Pathology and Dermatology October 2010

2. 86-year-old female pimple-like lesion that grew to pea-sized on her right cheek outside biopsy revealed a malignant tumor referred to University of Michigan for further treatment Case History

7. Diagnosis: Primary cutaneous neuroendocrine (Merkel cell) carcinoma

8. Merkel Cell Carcinoma (MCC) Background • Rare tumor – 1500 new cases per year in US • Incidence tripled over past 2 decades • Aggressive clinical course: • Local recurrence (40%) • Regional metastasis (50%) • Distant metastasis (33%) • Survival rates • 72% at 2 years • 29-64% at 5 years • More aggressive than melanoma

9. Merkel cell carcinoma (MCC) Clinical Features • Predilection for sun-damaged skin: • Head & neck - 50% • Extremities - 40% • Trunk, buttocks, genitalia – 10% • Elderly (5% < 50; exceedingly rare in childhood) • Caucasians • Immunosuppression (10%) – Organ transplant, CLL, HIV • Rapidly growing non-descript skin nodule – MCC seldom in the clinical differential

10. MCC Histologic Features • Small round blue cell tumor in dermis; rarely in situ • Circumscribed, trabecular, or infiltrative growth pattern • Tumor necrosis • Small undifferentiated cells with minimal cytoplasm • Nuclear molding • Finely stippled, “salt and pepper” chromatin • Apoptotic figures • Mitotic figures • Tumor infiltrating lymphocytes • Lymphovascular invasion • Other tumor types (Squamous cell carcinoma)

11. small round blue cell tumor in dermis

12. pagetoid spread In situ Merkel cell carcinoma (very rare)

13. infiltrative growth circumscribed growth trabecular growth

14. tumor necrosis

15. finely stippled “salt and pepper” chromatin

16. nuclear molding

17. mitoses apoptoses

18. tumor cells (arrows) obscured by TILs MCC with brisk tumor infiltrating lymphocytes

19. endothelial cells

20. SCC in situ (Bowen’s disease) MCC

21. rosettes

22. MCC Immunohistochemistry positive • Pancytokeratins • CAM5.2 • CK20 • Neuroendocrine markers – chromogranin A, synaptophysin, neuron-specific enolase, CD56 • TdT negative • Thyroid transcription factor (TTF)-1 • Mammalian achaete-scute complex (MASH)-1 cytoplasmic, membranous, and/or perinuclear dot-like

23. CK cocktail CK20 CK20

24. CGA TTF-1

25. MCC DifferentialDiagnosis • Small round blue cell tumors: • Metastatic neuroendocrine carcinoma, ex: small cell carcinoma of lung • Malignant lymphoma • Small cell malignant melanoma • PNET/Ewing’s sarcoma • Embryonal rhabdomyosarcoma • Neuroblastoma • Basal cell carcinoma

26. Small Cell Carcinoma of Lung (SCC-L) transbronchial biopsy

27. SCC-L CK cocktail CK20 TTF-1

28. Basal Cell Carcinoma BCC MCC BCC may resemble MCC from low power especially in areas where cleft retraction is not observed

29. Basal Cell Carcinoma BCC MCC • Most cases of BCC are easily distinguished from MCC at high power: • peripheral palisading • lack of fine, “salt and pepper“chromatin • stromal mucin; cleft retraction

30. Immunostain results in the differential diagnosis of small round blue cell tumors MCC = Merkel cell carcinoma; MSCC = metastatic small cell carcinoma; ML = malignant lymphoma SCMM = small cell malignant melanoma; ES = Ewing’s sarcoma; PNET = primitive neuroectodermal tumor; ER = embryonal rhabdomyosarcoma; Neur = neuroblastoma CK = cytokeratin; CGA = chromogranin A; NSE = neuron-specific enolase; SYN = synaptophysin; TTF-1 = thyroid transcription factor-1; LCA = leukocyte common antigen; VIM = vimentin; ACT = actin DES = desmin

31. Immunostain results in the differential diagnosis of small round blue cell tumors MCC = Merkel cell carcinoma; MSCC = metastatic small cell carcinoma; ML = malignant lymphoma SCMM = small cell malignant melanoma; ES = Ewing’s sarcoma; PNET = primitive neuroectodermal tumor; ER = embryonal rhabdomyosarcoma; Neur = neuroblastoma CK = cytokeratin; CGA = chromogranin A; NSE = neuron-specific enolase; SYN = synaptophysin; TTF-1 = thyroid transcription factor-1; LCA = leukocyte common antigen; VIM = vimentin; ACT = actin DES = desmin

32. Immunostain results in the differential diagnosis of small round blue cell tumors MCC = Merkel cell carcinoma; MSCC = metastatic small cell carcinoma; ML = malignant lymphoma SCMM = small cell malignant melanoma; ES = Ewing’s sarcoma; PNET = primitive neuroectodermal tumor; ER = embryonal rhabdomyosarcoma; Neur = neuroblastoma CK = cytokeratin; CGA = chromogranin A; NSE = neuron-specific enolase; SYN = synaptophysin; TTF-1 = thyroid transcription factor-1; LCA = leukocyte common antigen; VIM = vimentin; ACT = actin DES = desmin

33. Immunostain results in the differential diagnosis of small round blue cell tumors MCC = Merkel cell carcinoma; MSCC = metastatic small cell carcinoma; ML = malignant lymphoma SCMM = small cell malignant melanoma; ES = Ewing’s sarcoma; PNET = primitive neuroectodermal tumor; ER = embryonal rhabdomyosarcoma; Neur = neuroblastoma CK = cytokeratin; CGA = chromogranin A; NSE = neuron-specific enolase; SYN = synaptophysin; TTF-1 = thyroid transcription factor-1; LCA = leukocyte common antigen; VIM = vimentin; ACT = actin DES = desmin

34. Immunostain results in the differential diagnosis of small round blue cell tumors MCC = Merkel cell carcinoma; MSCC = metastatic small cell carcinoma; ML = malignant lymphoma SCMM = small cell malignant melanoma; ES = Ewing’s sarcoma; PNET = primitive neuroectodermal tumor; ER = embryonal rhabdomyosarcoma; Neur = neuroblastoma CK = cytokeratin; CGA = chromogranin A; NSE = neuron-specific enolase; SYN = synaptophysin; TTF-1 = thyroid transcription factor-1; LCA = leukocyte common antigen; VIM = vimentin; ACT = actin DES = desmin

35. Immunostain results in the differential diagnosis of small round blue cell tumors MCC = Merkel cell carcinoma; MSCC = metastatic small cell carcinoma; ML = malignant lymphoma SCMM = small cell malignant melanoma; ES = Ewing’s sarcoma; PNET = primitive neuroectodermal tumor; ER = embryonal rhabdomyosarcoma; Neur = neuroblastoma CK = cytokeratin; CGA = chromogranin A; NSE = neuron-specific enolase; SYN = synaptophysin; TTF-1 = thyroid transcription factor-1; LCA = leukocyte common antigen; VIM = vimentin; ACT = actin DES = desmin

36. MCC Prognostic Factors • Clinical stage (most important) • Clinical size <2cm (stage I); ≥2cm (stage II) • Regional lymph node involvement (stage III) • Distant metastasis (stage IV) • Histologic features • Tumor size (doesn’t correlate well with clinical size) • Tumor depth (anatomical compartment) • Growth pattern • Mitotic rate • Tumor infiltrating lymphocytes • Lymphovascular invasion

37. MCC of Unknown Primary • Approximately 5 – 10 % of MCC may involve lymph nodes or visceral sites without a known skin primary • Hypotheses: • Regression of a primary skin tumor (role of TILs) • Origin from occult Merkel cell(s) or pluripotent cell(s) at site

38. Merkel Cell Polyomavirus (MCPyV) • Discovered in 2008 by Feng et al. • Digital transcriptome subtraction of 2 libraries of cDNA transcripts derived from extracted mRNA from 1 MCC and 3 pooled MCCs revealed fusion transcript between novel polyomavirus T antigen and human receptor tyrosine phosphatase Feng H, et al. Science 319: 1096–1100, 2008

39. MCPyV • Sequencing led to a new polyomavirus - MCPyV • MCPyV + in: • 8 /10 additional MCC + for MCPyV • 5/59 control specimens from variety of body sites • 4/25 control skin specimens • Demonstrated clonal integration of MCPyV in 6 of 8 MCCs (early event) Feng H, et al. Science 319: 1096–1100, 2008

40. small circular double-stranded DNA polyomavirus • most closely related to the African green monkey polyomavirus • 3 structural (viral coat) proteins: VP1, VP2 and VP3 • 2 early tumor antigens: small T and large T Feng H, et al. Science 319: 1096–1100, 2008

41. MCPyV Immunohistochemistry • MCPyV large T-antigen - clone CM2B4 (Santa Cruz Biotechnologies)

42. MCPyV

43. MCPyV Additional Studies • MCPyV detected by IHC in: • 27/36 (75%) MCC – 12 primary & 15 mets • 0/26 pulmonary neuroendocrine (16 small cell and 10 large cell) carcinomas • 0/7 combined MCC and squamous cell carcinoma of skin (both components IHC-) Busam KJ et al. Am J Surg Pathol 33: 1378-1385, 2009

44. MCPyV Additional Studies • MCPyV detected by PCR on FFPE tissues in 1/74 visceral neuroendocrine carcinomas (32 lung, 16 GI, 20 GYN, 3 soft tissue, 2 head/neck, 1 bladder) • Positive sample was a pulmonary tumor and the patient was later discovered to have a MCC of buttock – CPC = metastatic MCC Duncavage EJ et al. Am J Surg Pathol 33: 1771-1777, 2009

45. MCPyV Additional Studies • 4 MCC cell lines (3 MCPyV+; 1MCPyV-): • Knocked down MCPyV T antigen using 3 different short hairpin RNA –expressing vectors against exon 1 of T antigen • Results: • All 3 MCPyV+ MCC cell lines demonstrated growth arrest and/or cell death • MCPyV- MCC cell line was unaffected • Conclusion: experimental evidence that T antigen expression is necessary for maintenance of MCPyV+ MCC and its etiologic role in MCPyV+ MCC Houben R et al. J Virol 84; 7064-7072, 2010

46. Conclusions • MCC is a rare yet aggressive cutaneous neoplasm that is increasing in incidence • Significant subset of patients are immunosuppressed • Cytomorphologic features of tumor cells can usually separate MCC from other small round blue cell tumors except for metastatic neuroendocrine carcinomas and rare cases of melanoma • Immunohistochemical panel [CK, CK20, neuroendocrine markers, TTF-1, others (LCA, S-100, CD99, actin/desmin)] plays an important role in definitive diagnosis and exclusion of histologic simulants • Novel polyomavirus has recently been discovered that appears to have a causative role in at least a subset of tumors

47. Questions?