An elderly male farmer presents with a 0.6 inch (1.5 cm) long, oval, pearly nodule on the lower eyelid. What is the most likely diagnosis?

The most likely diagnosis in this scenario is basal cell carcinoma, particularly considering the characteristics of the lesion described. Basal cell carcinoma often presents as a pearly nodule, particularly in sun-exposed areas of the skin, such as the lower eyelid of an elderly male farmer who may have had significant sun exposure throughout his life.

The lesion's size and description are typical for basal cell carcinoma, which is known for appearing as a small, shiny, and firm bump. Other common features can include the development of teleangiectasias (small, dilated blood vessels) at the surface.

In contrast, actinic keratosis typically appears as rough, scaly patches and would not present as a smooth, pearly nodule. A chancre of syphilis is usually associated with a painless ulcer rather than a nodule and would not be described as pearly. Dermatofibromas usually appear as firm nodules with a brownish hue and lack the pearly characteristics associated with basal cell carcinoma.

Thus, the clinical presentation aligns well with basal cell carcinoma, making it the most fitting diagnosis.