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Tissue polypeptide antigen as a putative indicator of apoptosis.

Tissue polypeptide antigen (TPA) is a keratin-derived product containing fragments of cytokeratins (CKs) 8, 18, and 19 (1) . The determination of serum TPA has been used in the management of cancer patients (2)(3) . TPA has also been measured in tissue extracts (4)(5) . In our experience, high TPA contents in the cytosols of breast cancer specimens were associated with longer relapse-free periods and overall survival rates (4) . This was an unexpected relationship and seemed not to be supported by a clear biological rationale.

It has been assumed that during mitosis the mother cell expels its cytokeratin in a degraded form to the cellular environment. This behavior may explain both the high serum cytokeratins in more aggressive tumors and the lower cytosolic TPA found in tumors with a worse prognosis. Because the reconstruction of cytoskeleton takes place soon after cell division, the latter hypothesis regarding tissue cytokeratin distribution was considered poorly tenable (6) . Moreover, the release of TPA from …