Histology of metastatic adenocarcinoma
The histology of metastatic adenocarcinoma may show a number of patterns. Low power view frequently shows a poorly circumscribed infiltrating tumour centred on the dermis (Figure 1). Cords and nodules of atypical epithelial cells can be seen dissecting between collagen bundles (Figure 2). These may show evidence of duct or gland formation (Figure 3), and may be set in a mucinous stroma (Figure 4). Vascular and lymphatic permeation may be evident in the telangiectoides and erysipeloides variants of breast metastases.
Metastatic adenocarcinoma pathology
Special stains and differential diagnosis of metastatic adenocarcinoma
While there is no substitute for clinical correlation and staging investigations, immunohistochemistry can provide clues to the site of origin, and help discriminate from primary cutaneous adnexal tumours. While never entirely specific, general rules are outlined below.
- P63: Positive more commonly in primary cutaneous adnexal tumours.
- CK7-/CK20+: Suggestive of gastrointestinal origin
- CK7+/CK20-: Suggestive of lung origin
- CK7: Focal staining suggestive of primary cutaneous adnexal tumour vs strong and diffuse staining in metastatic adenocarcinoma
- CK 5/6: Negative staining infrequently seen in primary cutaneous tumours
- CDX2: Suggests gastrointestinal origin
- Villin: Gastrointestinal, pancreatic or biliary origin.
- ER, PR and GCDFP: Favour breast origin. Note that all have been seen expressed in primary adnexal tumours and metastatic lesions can lose staining ability.
- Mammaglobin: Diffuse staining favours metastatic breast. Scattered positivity can be seen in primary cutaneous adnexal tumours.
- PSA and prostatic acid phosphatase: Support prostatic origin
- Podoplanin (D240): Negative staining suggests a metastatic lesion