Spindle Cell Squamous Cell Carcinoma of Head and Neck Region: a Clinicopathological and Immunohistochemical Study.

Spindle cell squamous cell carcinoma (SCSCC) represents a rare, dedifferentiated form of conventional squamous cell carcinoma (SCC) with propensity for head and neck. Morphological heterogeneity of this tumor poses significant diagnostic challenge for pathologists. This study aimed to evaluate detailed morphological and immunohistochemical (IHC) characteristics of a series of SCSCC cases. All head and neck SCSCCs diagnosed over seven years were retrospectively analyzed to assess morphological features in detail with evaluation of possible differential diagnoses. Elaborate IHC panel was performed in each case. Eleven cases (8 males, 3 females) were included. Most patients were in 5th to 7th decade. Oral cavity (n = 6; 54.5%); oropharynx (n = 3; 27.3%), and larynx (n = 2; 18.9%) were involved. Tumors were polypoidal (n = 6), ulceroproliferative (n = 3), or ulceroinfiltrative (n = 2). Microscopically, epithelial ulceration was common (90.9%). Squamous differentiation was evident on light microscopy in 6 (54.5%) cases as surface dysplasia (n = 1; 9.1%), infiltrative tumor (n = 4; 36.4%), or both (n = 1; 9.1%). The spindled tumor component showed markedly heterogeneous morphology mimicking mesenchymal malignancies or benign mesenchymal proliferations. IHC for epithelial markers (CK, EMA, p40, and p63) established epithelial differentiation in 40% (2 of 5) cases where it was not evident morphologically. CK showed highest positivity followed by p40 and p63. Aberrant mesenchymal marker expression was variably seen. Morphological diagnosis of SCSCC is challenging with several histological mimics. Surface dysplasia and component of invasive SCC in a predominantly spindled tumor are important subtle morphological clues. Systematic morphological approach aided by IHC is helpful in clinching the accurate diagnosis. © Indian Association of Surgical Oncology 2021.