Due to the rarity of<unk> D and lack of clinical knowledge, the<unk>  is not very commonly diagnosed. Patients are often misdiagnosed with eczema or dermatitis and a delay of 2 years is expected from the onset of symptoms before a definitive diagnosis has been reached. It is important to include that the lesion is associated with another cancer. A biopsy will establish the diagnosis. Punch biopsies are not effective in differentially diagnosing for<unk> D and as a result, excisional biopsies of the affected area are taken XX. A positive test result for<unk> D shows increased numbers of large polygonal cells with a pale bluish cytoplasm, large nucleus and nucleolus, infiltrating the epidermal layer. These neoplastic cells can be found singly scattered or can appear in groups called nests.<unk>  cells contain mucin and cytokeratins which can be used in the diagnosis of<unk> D 8 MUC5A2 is found in<unk> D of the vulvar and male genitalia regions whereas MUC2 is expressed in perianal<unk> D. Loss of MUC5A2 can indicate an invasive spread. Immunohistochemistry (IHC) can be used to determine whether<unk> D is either primary or secondary. Primary<unk> D tests positive for CK7 but negative for CK20, whereas secondary is positive for both. Lack of positivity for hormone receptors and HER2 protein is overexpressed meaning that the cells are dividing rapidly and can be indicate an aggressive and more recurrent<unk> . Classification Primary<unk> D is of cutaneous origins and is found within the epidermis or the underlying apocrine glands. Although it is limited to the epithelium, it has potential to spread and progress into an invasive tumour, metastasising to the local lymph nodes and distant organs. This form of<unk> D is not associated with an adenocarcinoma. The secondary form results due to an underlying adenocarcinoma spreading to the epidermis. Similar to the primary form, if secondary<unk> D invades the dermis, the neoplastic cells can metastasise to the lymph nodes and in some cases, the dermis. According to the Wilkinson and Brown subclassification system, there are 3 subtypes for each classification. +Table 1. Sub-classifications of primary and secondary<unk><unk>  Primary (cutaneous) Secondary (non-cutaneous) Intraepithelial cutaneous<unk><unk>  of the usual type Anorectal Intraepithelial cutaneous<unk><unk>  with invasion Urothelial Intraepithelial cutaneous<unk><unk>  as a manifestation of underlying adenocarcinoma of skin appendage Other
Extramammary Paget's disease
Acral lentiginous melanoma
Arsenical keratosis
Acral fibrokeratoma
Hydrocarbon keratosis
Seborrheic keratosis
Lentigo maligna melanoma
Actinic keratosis