The clinical appearance of the eruption, coupled with onset in the second decade, nail involvement, and specific cutaneous site distribution all suggest the correct answer: psoriasis. Psoriasis affects 0.2% to 3% of the world’s population, with wide variation in prevalence among different geographic and ethnic groups. Psoriasis is now thought of as the cutaneous manifestation of a systemic inflammatory process, with the skin disorder being the initiator or amplifier of a cytokine-driven set of comorbidities. The latter potentially include any or all of the components of the metabolic syndrome, chronic obstructive pulmonary disease (even in the absence of smoking), and neoplasia. In fact, while individuals almost never die from the skin disease itself, psoriatics have long been known to be at increased risk for early mortality related to comorbidities.[2,3]
Among the comorbid conditions associated with psoriasis is malignancy. Studies in Western countries strongly suggest that the development of lymphoma is more likely in the population subset affected by psoriasis, while epidemiologic investigations from other parts of the world do not support this assertion.[4,5] Many other papers have linked psoriasis to a large number and wide variety of malignant neoplasms, including cancers of the lung, oropharynx, colon, liver, breast, and genitalia.[2,4,6-10] Certainly, underlying genetic differences, varied living conditions, variable dietary preferences and social mores, differing regional treatment patterns, and different study designs (hospital-based vs population-based) probably all contribute to the discrepancies observed in the available literature. If any reliable assertions can be made, I suggest that the following three statements can reasonably be considered to be true: 1) Consider every psoriasis patient at risk for the premature development of cancer, especially when the disease is severe and has an early age of onset. 2) Consider that the most likely cancers to occur in those at risk are the neoplasms most inherently prevalent in the population from which the patient comes. 3) The presence of additional, known comorbid conditions (eg, smoking, diabetes) may even further elevate cancer risk.
Thus, in the case at hand, a relatively young patient with long-standing severe psoriasis (> 10% body surface area) is clearly in an at-risk population. The presence of diabetes augments the basic risk factor of psoriasis. The acute onset of substantial weight loss, associated with notable fatigue, should immediately raise the index of suspicion in the clinician. The dermatologist ordered the most rudimentary cancer screening while submitting a consult to oncology: complete blood cell count, fecal occult blood, chest radiograph, prostate-specific antigen level, and urinalysis. The patient was found to be anemic, and three of three stool specimens were positive for occult blood. Subsequent additional evaluation disclosed Duke’s C2 class moderately well-differentiated adenocarcinoma of the colon. The cancer eventually was responsible for the patient’s death.
Was this entirely unexpected? The answer to this rhetorical question is clearly “no.” Cancers of the digestive tract, especially the colon and liver, are among the most common encountered in the Taiwanese population (population incidence rate of approximately 1.6%), with the rate increasing dramatically after age 40. Moreover, a recent publication verified that among Taiwanese psoriatics, digestive tract carcinomas are those most likely to appear; this likelihood is increased with the concurrent presence of diabetes. In the latter study, it was further demonstrated that both psoriasis and type 2 diabetes are independent risk factors for the development of digestive tract cancers for the 41- to 60-year-old age group of native Taiwanese. Thus, the patient presented was at significant risk for this unfortunate event. Although there was no delay in instituting appropriate evaluation once the patient presented with symptoms, perhaps he might have been warned earlier about his at-risk status, thereby facilitating an earlier request for medical attention.