Breast cancer is the second most common malignancy in women (after primary skin cancer) and is the second leading cause of cancer-related death in this population. In 2020, the American Cancer Society reported an estimated 276,480 new breast cancer diagnoses and 42,170 breast cancer–related deaths.1 Despite the fact that routine screening with mammography and sonography is standard, the incidence of advanced breast cancer at the time of diagnosis has remained stable over time, suggesting that life-threatening breast cancers are not being caught at an earlier stage. The number of breast cancers with distant metastases at the time of diagnosis also has not decreased.2 Therefore, although screening tests are valuable, they are imperfect and not without limitations.
Cutaneous metastasis is defined as the spread of malignant cells from an internal neoplasm to the skin, which can occur either by contiguous invasion or by distant metastasis through hematogenous or lymphatic routes.3 The diagnosis of cutaneous metastasis requires a high index of suspicion on the part of the clinician.4 Of the various internal malignancies in women, breast cancer most frequently results in metastasis to the skin,5 with up to 24% of patients with metastatic breast cancer developing cutaneous lesions.6
In recent years, there have been multiple reports of skin lesions prompting the diagnosis of a previously unknown breast cancer. In a study by Lookingbill et al,6 6.3% of patients with breast cancer presented with cutaneous involvement at the time of diagnosis, with 3.5% having skin symptoms as the presenting sign. Although there have been studies analyzing cutaneous metastasis from various internal malignancies, none thus far have focused on cutaneous metastasis as a presenting sign of breast cancer. This systematic review aimed to highlight the diverse clinical presentations of cutaneous metastatic breast cancer and their clinical implications.
This study utilized the PRISMA guidelines for systematic reviews.7 A review of the literature was conducted using the following databases: MEDLINE/PubMed, EMBASE, Cochrane library, CINAHL, and EBSCO.
Search Strategy and Analysis
We completed our search of each of the databases on December 16, 2017, using the phrases cutaneous metastasis and breast cancer to find relevant case reports and retrospective studies. Three authors (C.J., S.R., and M.A.) manually reviewed the resulting abstracts. If an abstract did not include enough information to determine inclusion, the full-text version was reviewed by 2 of the authors (C.J. and S.R.). Two of the authors (C.J. and M.A.) also assessed each source for relevancy and included the articles deemed eligible (Figure 1).
Inclusion criteria were the following: case reports and retrospective studies published in the prior 10 years (January 1, 2007, to December 16, 2017) with human female patients who developed metastatic cutaneous lesions due to a previously unknown primary breast malignancy. Studies published in other languages were included; these articles were translated into English using a human translator or computer translation program (Google Translate). Exclusion criteria were the following: male patients, patients with a known diagnosis of primary breast malignancy prior to the appearance of a metastatic cutaneous lesion, articles focusing on the treatment of breast cancer, and articles without enough details to draw meaningful conclusions.
For a retrospective review to be included, it must have specified the number of breast cancer cases and the number of cutaneous metastases presenting initially or simultaneously to the breast cancer diagnosis. Bansal et al8 defined a simultaneous diagnosis as a skin lesion presenting with other concerns associated with the primary malignancy.