Metastases are tumours that have spread from elsewhere and are separate from the initial (primary) lesion; usually, they are an ominous finding.
Metastases are not always obvious when encountered; thus, metastasis should be considered with every diagnosis of a malignant tumour.
Seen from pathology, metastatic disease and direct extension of a tumour (on a biopsy) may be indistinguishable. Collectively, they may also be referred to as secondary tumours.
Cancers of unknown primary are dealt with in the cancer article. A general approach to undifferentiated tumours is given in the basics article under the heading modified general morphologic DDx of malignancy.
A handful of things have metastatic-like behaviour but are not malignant. Examples of benign things with metastatic-like behaviour are: benign metastasizing leiomyoma, endometriosis, endosalpingiosis and benign nevus cells (in lymph nodes).
- It is called "in-transit", as it happens while the tumour is on the way to the regional lymph node.
- If a separate tumour nodule is close to the primary tumour, it is known as satellitosis.
- The definitions vary based on the primary site.
- Dependent on (suspected) primary.
Not necessary to do stains/immunostains if all of the following are true:
- A primary is already established by pathology.
- The morphology of the lesion is compatible with the established primary.
- The clinical impression is a metastasis.
- The suspected primary is not breast.
- ASCO/CAP guidelines state that ER and PR (in breast cancer recurrences) should always be re-tested.
This depends somewhat on the tumour. A synoptic is not done. Margin status should be commented on. A morphologic description is useful if a subsequent resection is done.
SMALL BOWEL, RESECTION: - METASTATIC ADENOCARCINOMA, SEE COMMENT. - SURGICAL MARGINS NEGATIVE FOR MALIGNANCY. COMMENT: The tumour involves only the outer aspect of the bowel wall; the bowel mucosa is not involved. The tumour consists of glands with cuboidal tumour cells that have a moderate quantity of pale cytoplasm, and round nuclei. The tumour is moderately differentiated.
VERTEBRAL LESION, L1, BIOPSY: - ADENOCARCINOMA -- PENDING IHC.
LESION OF T7 VERTEBRA, CORE BIOPSY: - METASTATIC CARCINOMA, CONSISTENT WITH BREAST PRIMARY, SEE COMMENT. COMMENT: The morphology is compatible with a metastatic breast carcinoma. The tumour cells stain as follows: POSITIVE: CK7, ER, PR, MAMMOGLOBIN. NEGATIVE: CK20, TTF-1, CDX2, HER2, GCDFP. The immunostaining profile is compatible with a metastatic breast carcinoma. ER, PR and HER2 are interpreted as Class I IHC tests (results used by pathologists), as per the CAP classification. 1. Am J Clin Pathol 133 (3):354-65.
Probable lung metastasis
The sections show atypical cohesive cuboidal-to-low columnar cells with moderate nuclear pleomorphism. The nuclei are round/ovoid and eccentrically placed in the cell. Nucleoli of moderate size are identified. Mitotic figures are present. The cytoplasm is lightly eosinophilic and vacuoles are seen focally.
- Pitts, S.; Oberstein, EM.; Glassberg, MK. (Jun 2004). "Benign metastasizing leiomyoma and lymphangioleiomyomatosis: sex-specific diseases?". Clin Chest Med 25 (2): 343-60. doi:10.1016/j.ccm.2004.01.014. PMID 15099894.
- Cook, MG. (Oct 2004). "Benign melanocytic lesions mimicking melanomas.". Pathology 36 (5): 414-8. doi:10.1080/00313020412331283842. PMID 15370110.
- Puppa, G.; Ueno, H.; Kayahara, M.; Capelli, P.; Canzonieri, V.; Colombari, R.; Maisonneuve, P.; Pelosi, G. (Mar 2009). "Tumor deposits are encountered in advanced colorectal cancer and other adenocarcinomas: an expanded classification with implications for colorectal cancer staging system including a unifying concept of in-transit metastases.". Mod Pathol 22 (3): 410-5. doi:10.1038/modpathol.2008.198. PMID 19136930.
- Hammond, ME.; Hayes, DF.; Dowsett, M.; Allred, DC.; Hagerty, KL.; Badve, S.; Fitzgibbons, PL.; Francis, G. et al. (Jul 2010). "American Society of Clinical Oncology/College of American Pathologists guideline recommendations for immunohistochemical testing of estrogen and progesterone receptors in breast cancer (unabridged version).". Arch Pathol Lab Med 134 (7): e48-72. doi:10.1043/1543-2165-134.7.e48. PMID 20586616.