SIN, not KIN.

Copyright J Cutan Pathol 2009: 36: 820 John Wiley & Sons. Printed in Singapore 2009 John Wiley & Sons A/S Journal of Cutaneous Pathology Letter to the Editor SIN, not KIN To the Editor, The diagnosis of in situ cutaneous squamous lesions is controversial and suffers from lack of re- producibility between dermatopathologists. Ramos- Ceballos et al. 1 present a study on the diagnostic concurrence between dermatopathologists utilizing a three-tiered system of grading referred to as keratinocytic intraepithelial neoplasia (KIN). While these authors show a moderate degree of concur- rence between pathologists using their system, this terminology is awkward and unlikely to become widely accepted. Alternatively, we prefer the usage of the term squamous intraepithelial neoplasia (SIN), previously proposed by Callen and Headington, 2 which emphasizes the analogy to cervical intra- epithelial neoplasia (CIN) and vulvar intraepithelial neoplasia (VIN). Pathologists do not refer to squamous cell carcinoma in situ (SCCis) as Okerati- nocytic cell carcinoma in situ’, nor do we refer to invasive squamous cell carcinoma (SCC) as Okerati- nocytic cell carcinoma’, and we doubt that the authors propose such replacement of these com- monly accepted terms. Therefore, given that these terms are strongly ingrained in dermatopathology, the usage of the terminology SIN is more appropri- ate than KIN, and clearly emphasizes the overlap between SIN and SCCis. In addition, while the authors argue that SIN is a less specific term than KIN, SIN is clearly more specific than the widely used terms CIN and VIN, which both refer to the respective organ systems, rather than the cell types, involved. In this proposed classification, lesions formerly diagnosed as actinic keratosis (AK) or solar keratosis, where the atypia is confined to the basal one third of the epidermis, would be graded as SIN 1, while lesions with atypia involving half to two thirds of the epidermis (i.e., bowenoid AK) would be referred to as SIN 2. SCCis, defined by full-thickness epidermal atypia (i.e., Bowen’s disease), would be diagnosed as SIN 3 in this system. This terminology does not presuppose a progression of in situ neoplasia from SIN 1 to SIN 2 to SIN3, as most cases of Bowen’s disease likely represent a separate (de novo) process from AK and bowenoid AK. In addition, it is well established that most invasive SCCs arise in AKs (SIN 1/SIN 2), 3 not in Bowen’s disease (SIN 3), although the later is associated with a more aggressive form of invasive SCC. 4 Therefore, while the pathophysiologic and clinical implications would differ between SIN grades, the SIN terminology would represent a simplified, and perhaps more re- producible, classification compared with the cur- rently used terminology. While this system may not become widely accepted soon, it is clearly preferable to, and more likely to be adapted, than the KIN terminology. David S. Cassarino 1 , MD, PhD Ronald J. Barr 2 , MD Department of Pathology, University of California, Los Angeles, CA, USA and Department of Dermatopathology, University of California, Irvine, CA, USA e-mail: dsc9w@yahoo.com References 1. Ramos-Ceballos FI, Ounpraseuth ST, Horn TD. Diagnostic concordance among dermatopathologists using a three-tiered keratinocytic intraepithelial neoplasia grading scheme. J Cutan Pathol 2008; 35: 386. 2. Callen JP, Headington J. Bowen’s and non-Bowen’s squamous intraepidermal neoplasia of the skin. Relationship to internal malignancy. Arch Dermatol 1980; 116: 422. 3. Cassarino DS, DeRienzo D, Barr RJ. Cutaneous squamous cell carcinoma: a comprehensive classification system. Part I. J Cutan Pathol 2006; 33: 191. 4. Cassarino DS, DeRienzo D, Barr RJ. Cutaneous squamous cell carcinoma: a comprehensive classification system. Part II. J Cutan Pathol 2006; 33: 261.