Expression of STAT1 and STAT2 in malignant melanoma does not correlate with response to interferon-alpha adjuvant therapy

Abstract

Interferon-alpha (IFN-alpha) is used as an adjuvant therapy in patients with malignant melanoma and who have undergone surgical resection of high-risk lesions. Defective expression or activation of STAT1 or STAT2 has been shown to correlate with IFN-alpha or resistance in vitro; however, recent data from our laboratory suggest that the anti-tumor effects of IFN-alpha are dependent on STAT1 signaling within host immune cells. We measured STAT1 and STAT2 expression in 28 melanoma biopsies (8 cutaneous lesions; 1 lung metastasis; 19 nodal metastases) obtained from patients prior to the initiation of adjuvant IFN-alpha therapy. Disease recurrence following IFN-alpha treatment did not correlate with the staining intensity of either STAT1 (P = 0.61) or STAT2 (P = 0.52). Tumors with minimal STAT1 or STAT2 expression (< 20% positive) were present in four patients with tumor-positive lymph nodes, who exhibited prolonged relapse-free survival (> 44 months) following adjuvant therapy. Conversely, high levels of STAT1 were present in a patient who recurred during the course of IFN-alpha therapy. A case study of one patient who experienced recurrent disease during IFN-alpha treatment revealed that STAT1 levels were greater in the recurrent tumor when compared to the original lesion. These studies provide direct evidence to suggest that levels of STAT1 and STAT2 within the tumor do not influence a patient's response to adjuvant IFN-alpha.

Fig. 1

Representative STAT1 staining from a melanoma positive lymph node. Strong cytoplasmic and nuclear staining of STAT1 was observed in both melanoma cells and mononuclear cells present in the lymph nodes. a Representative tumor-infiltrated lymph node magnified at 200×, b Representative tumor-infiltrated lymph node magnified at 400×, (c) Representative mononuclear cells magnified at 800×

Fig. 2

STAT1 staining. Representative STAT1 staining from malignant melanoma lesions showing a strong cytoplasmic staining b strong nuclear and cytoplasmic staining or c samples stained with a control murine IgG antibody (negative control). All sections shown are magnified at 400×

Fig. 3

STAT2 Staining. Representative STAT2 staining from malignant melanoma lesions showing a, b strong cytoplasmic staining and c strong nuclear staining. All sections shown are magnified at 400×

Fig. 4

Immunohistochemical staining of malignant melanoma from a patient exhibiting recurrent disease during IFN-α2b adjuvant therapy. Tumor tissue was obtained prior to IFN-α2b adjuvant therapy (initial nodal lesion) and from the lesion that developed at the site of the wide local excision on the calf during IFN-α2b treatment. Sections from each tumor were stained by hematoxylin and eosin, or with anti-STAT1, -STAT2 or appropriate isotype control antibodies (mouse IgG or rabbit IgG). All panels represent tumor as seen at 600× magnification. Analysis indicated the presence of a polymorphonuclear cell (PMN) infiltrate in viable tumor (see H and E panels), consistent with inflammation and tumor cell necrosis. No substantial background staining was observed with isotype control antibodies while cytoplasmic staining was observed for STAT1 and STAT2 in all panels