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Abstract
Renal cell carcinomas represent about 1% to 3% of visceral cancers and account for 85% of renal cancers in adults. The median age is 55 years and male predominance is 2: 1 (McLaughlin et al., 2000).
Two decades ago there was a tendency to lump all renal neoplasms thought to be of epithelial origin (except urothelial carcinoma of the renal pelvis) occurring in adults together, regardless of the morphology. The discoveries of the past two decades have proven that a variety of well-defined neoplasms with characteristic patterns of genetic abnormality were contained within what previously had been simply as “renal cell neoplasms” (Eble, 1998b).
More progress has been made in the histogenesis of renal cell carcinoma. In the nineteenth century, the predominant theory of oncogenesis held that neoplasms arose from heterotopic embryonic tissue that attempted to recapitulate mature organs at abnormal sites. Under the influence of this concept, Grawitz in (1883) proposed the term hypernephroma to describe the histogenesis renal carcinomas from heterotopic adrenal rests in the kidneys (Farrow, 1989).
Keratins are intermediate filament proteins, which are constituents of the mammalian epithelial cytoskeleton. At least 20 different types have been discriminated in various tissues on the basis of molecular weight and isoelectric pH values. In intermediate filaments, they are present as pairs of type-I (acidic) and type-II (neutral to basic) proteins. Different subsets are expressed by different epithelia, and these patterns are largely retained during neoplastic transformation. Hence, epithelia (simple and complex) and epithelial tumors can be classified on the basis of keratin protein expression (Langner et al., 2004).
In particular, cytokeratins 7 & 20 have generated interest because of their well-recognized utility in determining the site of origin of metastatic carcinomas of unknown origin (Wu et al., 2002). Published reports on cytokeratin 7 immunostaining in renal epithelial neoplasms are conflicting (Langner et al., 2004). Generally, in some series, cytokeratin 7 expression is thought to be infrequent in renal cell carcinoma (Chu et al, 2000), in other series, cytokeratin 7 is commonly present in the papillary subtypes (Leroy et al., 2000). However, others concluded that cytokeratin 7 may be useful in the differential diagnosis of chromophobe RCC from renal oncocytomas (Leroy et al., 2000) & (Kim et al., 2002).
Although studies describe an almost complete lack of CK20 positivity in RCC (Langner et al, 2004) (Kim et al., 2002), & Stoprya et al., (2001), reported that CK20 staining in oncocytomas demonstrated 80% positivity with variable patterns and distribution.
In fact the general lack of cytokeratin 20 expression in renal tubular malignancies was suggested as a criterion for differential diagnosis (Han. 1999). However, Kim et al. (2002) reported 20% of papillary RCC showing cytokeratin 20 expressions.