The antigens expressed by tumors have several sources; some are derived from oncogenic viruses like human papillomavirus, which causes cancer of the cervix, vulva, vagina, penis, anus, mouth, and throat, while others are the organisms own proteins that occur at low levels in normal cells but reach high levels in tumor cells. One example is an enzyme called tyrosinase that, when expressed at high levels, transforms certain skin cells (for example, melanocytes) into tumors called melanomas. A third possible source of tumor antigens are proteins normally important for regulating cell growth and survival, that commonly mutate into cancer inducing molecules called oncogenes. The main response of the immune system to tumors is to destroy the abnormal cells using killer T cells, sometimes with the assistance of helper T cells. Tumor antigens are presented on MHC class I molecules in a similar way to viral antigens. This allows killer T cells to recognize the tumor cell as abnormal. NK cells also kill tumorous cells in a similar way, especially if the tumor cells have fewer MHC class I molecules on their surface than normal; this is a common phenomenon with tumors. Sometimes antibodies are generated against tumor cells allowing for their destruction by the complement system.Some tumors evade the immune system and go on to become cancers. Tumor cells often have a reduced number of MHC class I molecules on their surface, thus avoiding detection by killer T cells.
Ichthyosis acquisita is a disorder clinically and histologically similar to ichthyosis vulgaris. : 565

Presentation
Associated conditions
The development of ichthyosis in adulthood can be a manifestation of systemic disease, and it has been described in association with malignancies, drugs, endocrine and metabolic disease, HIV, infection, and autoimmune conditions. : 494 It usually is associated with people who have Hodgkins disease but it is also occurs in people with mycosis fungoides, other malignant sarcomas, Kaposis sarcoma and visceral carcinomas. It can occur in people with leprosy, AIDS, tuberculosis, and typhoid fever. See also
Ichthyosis
Confluent and reticulated papillomatosis of Gougerot and Carteaud
List of cutaneous conditions

References


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