Which of the following is a type of skin cancer that is likely to metastasize if not treated early?

A. Basal cell carcinoma is incorrect because it is the most common type of skin cancer but is generally slow-growing and rarely metastasizes. It primarily causes local tissue damage if untreated but has a very low risk of spreading to distant sites.

B. Melanoma is correct because melanoma is a malignant tumor of melanocytes and is highly aggressive. If not detected and treated early, melanoma can metastasize to lymph nodes and distant organs, including the liver, lungs, and brain. Early detection and surgical excision are critical to prevent spread and improve survival. Risk factors include excessive UV exposure, fair skin, a history of sunburns, and multiple moles.

C. Squamous cell carcinoma is incorrect because although it is malignant and can invade surrounding tissues, squamous cell carcinoma has a lower tendency to metastasize than melanoma. However, untreated lesions can become locally destructive and, in rare cases, metastasize to regional lymph nodes.

D. Actinic keratosis is incorrect because it is a precancerous lesion, not a true cancer. These rough, scaly patches result from chronic sun exposure and have the potential to progress to squamous cell carcinoma over time, but they are not inherently malignant or metastatic.

A. Bacterial overgrowth of highly contagious S. aureus with development of vesicles and pruritus is incorrect because this description applies to impetigo, which is a superficial bacterial skin infection. Psoriasis is an autoimmune condition and is not contagious, so bacteria are not the primary cause.

B. Abnormal T-cell activation leading to excessive growth of keratinocytes and rapid epidermal shedding is correct because psoriasis is driven by dysregulation of the immune system. In this condition, T-cells become overactive and release cytokines that stimulate keratinocyte proliferation at an accelerated rate. Normally, keratinocytes take about 28–30 days to mature and shed, but in psoriasis, this process can occur in 3–5 days. The rapid turnover results in thickened, scaly plaques, redness, and inflammation. Chronic inflammation also contributes to the pruritus, discomfort, and erythema seen in affected areas. Triggers such as stress, infections, or certain medications may exacerbate the condition but do not cause it directly.

C. Sensitization on first exposure to an allergen with rash development on subsequent exposure is incorrect because this describes allergic contact dermatitis, where the immune system reacts to a previously encountered allergen. Psoriasis, in contrast, is autoimmune and does not require prior allergen exposure. The lesions are caused by internal immune dysregulation, not external sensitization.

D. Latent virus becomes reactivated by infection or stress, leading to development of skin lesions is incorrect because this mechanism describes viral conditions such as shingles (herpes zoster). Psoriasis is not caused by a virus, and the plaques and scales result from keratinocyte hyperproliferation due to immune dysregulation rather than viral reactivation.