The correct answer is 4. A markedly high platelet count (thrombocytosis) is a manifestation of an occult neoplasm. Thrombocytosis can be classified into two main types:
1. Primary/essential: occurs due to abnormalities in the bone marrow, leading to the overproduction of platelets. It is considered a myeloproliferative disorder and is typically diagnosed based on criteria such as an elevated platelet count and the absence of underlying conditions that could explain the increase.
2. Secondary: caused by underlying medical conditions or factors that stimulate the bone marrow to produce more platelets. Examples include infections, inflammatory disorders, iron deficiency anemia, certain cancers (such as lung cancer or ovarian cancer), and asplenia (absence of the spleen).