Final answer:
The condition described as an erythematous scaling lesion of the breast involving the nipple and areola unilaterally with an underlying malignancy is identified as Paget's disease of the breast.
Step-by-step explanation:
The erythematous scaling lesion of the breast involving the nipple and areola unilaterally and associated with an underlying malignancy is identified as Paget's disease of the breast. This condition is a rare type of cancer that typically affects the skin of the nipple and areola, and it is often associated with ductal carcinoma in situ (DCIS) or invasive breast cancer. Paget's disease can be characterized by symptoms such as tingling, itching, redness, and flaky or scaly skin on the breast, particularly around the nipple and areola.