Letters to the Editor
To the Editor:
Recently, we have discovered the utility of OCT4 in the diagnosis of adrenal medullary derived neoplasms1 and various neuroendocrine neoplasms. We hypothesized that the same immunohistochemical staining pattern would be observed in Merkel cell carcinoma of the skin given that it is a type of cutaneous neuroendocrine tumor containing neurosecretory granules. To the best of our knowledge, the cytoplasmic OCT4 expression in Merkel cell carcinoma has not been previously studied.
OCT4, a transcription factor, has been useful in the diagnosis of germ cell tumors, showing a characteristic nuclear staining pattern for seminoma and embryonal carcinoma.2–5 Our institution sees a large number of patients with germ cell tumors and uses OCT4 on a regular basis for detecting metastatic embryonal carcinoma and seminoma. While reviewing retroperitoneal lymph node dissection cases, we have encountered paraganglionic tissue present within the specimen displaying an intense cytoplasmic OCT4-positive staining pattern with the monoclonal antibody.6 Further work with pheochromocytomas and neuroendocrine tumors has shown identical immunostaining findings.1
We reviewed 16 cases of Merkel cell carcinoma of the skin and recorded the amount of cytoplasm for each case (scant vs. moderate). “Scant” was defined as most tumor cells showing nuclear molding with imperceptible cytoplasm, and “moderate” was defined as most tumor cells with perceivable clear to eosinophilic cytoplasm. Monoclonal OCT4 (Cell Marque, Rocklin, CA) and polyclonal OCT4 (Santa Cruz Biotechnology, Santa Cruz, CA) immunostaining were performed on all cases, with each case evaluated for intensity and extent of positive reactivity with OCT4.
A summary of the immunohistochemical staining results is provided in Table 1. Fourteen of 16 cases expressed cytoplasmic OCT4 staining, ranging from weak to strong in intensity and 5%–100% in extent. Ten of 12 cases with moderate amount of cytoplasm showed at least moderate intensity, staining >20% of tumor cells (Fig. 1). Two of the 4 cases with scant cytoplasms showed moderate 5% staining and weak 10% staining, respectively (Fig. 2); the remaining 2 cases were completely negative. The adjacent squamous cells, adnexal structures, and basal cells showed no reactivity with OCT4 in neither nuclear nor cytoplasmic locations. All cases stained with polyclonal OCT4 antibody showed no nuclear or cytoplasmic staining.
Previous studies examining the sensitivity and specificity of OCT4 concluded that this antibody was most specific for identifying germ cell tumors, specifically intratubular germ cell neoplasia, seminoma, and embryonal carcinoma, and all positive staining was defined as nuclear reactivity.2–5 There was no report of any positive immunostaining of OCT4 with any cutaneous lesions in the literature.7 The antibody used in the previous studies is a polyclonal antibody (Santa Cruz Biotechnology), whereas at our institution, we have used a new OCT4 monoclonal antibody (Cell Marque) for diagnosing germ cell tumors, we encountered a new staining pattern of OCT4 cytoplasmic, in paraganglionic tissue, adrenal medullary derived tissue, and in various neuroendocrine tumors.1,6 We have documented through immunoelectron microscopy that the monoclonal antibody utilized in our laboratory for this particular study (Cell Marque) is directly interacting with the neurosecretory granules within the cytoplasm.1
A significant decrease or complete loss of the cytoplasmic reactivity with OCT4 while using a blocking peptide supports that this particular pattern of staining is true OCT4 immunoreactivity versus background staining. The comparative analysis with polyclonal OCT4 antibody demonstrated an absence of cytoplasmic staining in all cases. It has been observed that more differentiated the neuroendocrine tumor is the stronger the cytoplasmic staining is. It is noticed that small cell carcinoma stains weakly as compared with more differentiated carcinoid tumors and seems to be directly related to the number of neurosecretory granules in the cytoplasm. Additionally, the Ki67 proliferation index has been shown to be inversely related to the intensity of cytoplasmic staining.
In summary, monoclonal OCT4 stain is a sensitive marker for diagnosing Merkel cell carcinoma, and those with more cytoplasm compared with the classical “small cells” will show more diffuse and intense cytoplasmic OCT4 staining because of more neurosecretory granules in the modest amount of cytoplasm. A cytoplasmic OCT4 reactivity is valuable in diagnosing Merkel cell carcinoma.
1. Alexander R, Cheng L, Grignon DJ, et al.. Cytoplasmic staining of OCT4 is a highly sensitive marker of adrenal medullary derived tissue. Am J Surg Pathol. 2013;37:724–733.
2. Looijenga LH, Stoop H, de Leeuw HP, et al.. POU5F1 (OCT3/4) identifies cells with pluripotent potential in human germ cell tumors. Cancer Res. 2003;63:2244–2250.
3. Jones TD, Ulbright TM, Eble JN, et al.. OCT4: a sensitive and specific biomarker for intratubular germ cell neoplasia of the testis. Clin Cancer Res. 2004;10:8544–8547.
4. Jones TD, Ulbright TM, Eble JN, et al.. OCT4 staining in testicular tumors: a sensitive and specific marker for seminoma and embryonal carcinoma. Am J Surg Pathol. 2004;28:935–940.
5. Cheng L, Sung MT, Cossu-Rocca P, et al.. OCT4: biological functions and clinical applications as a marker of germ cell neoplasia. J Pathol. 2007;211:1–9.
6. Clevenger JA, Kum JB, Alexander RE, et al.. Paraganglion cells stain positively for OCT4: a potential pitfall in assessing retroperitoneal lymph node dissection specimens for germ cell tumour metastasis. Histopathology. 2013;62:360–363.
7. Katona TM, Billings SD, Montironi R, et al.. Expression of OCT4 transcription factor in cutaneous neoplasia. Appl Immunohistochem Mol Morphol. 2007;15:359–362.