Each of the WHO categories contains numerous descriptive subcategories of interest to the hematopathologist and oncologist; however, most of the clinically significant information in the WHO schema is communicated via categorization into one of the subtypes listed below. The revised fourth edition of the WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues was released in 2016. This classification, which is based on a combination of genetic and immunophenotypic markers and morphology, defines the subtypes of AML and related neoplasms as: In 2022 a new classification has been published. Acute leukemias of ambiguous lineage (also known as mixed phenotype or biphenotypic acute leukemia) occur when the leukemic cells can not be classified as either myeloid or lymphoid cells, or where both types of cells are present. French-American-British
The French-American-British (FAB) classification system provides terminology that is still sometimes used, and it remains a valuable diagnostic tool in areas without access to genetic testing, this system has largely become obsolete in favor of the WHO classification, which correlates more strongly with treatment outcomes.The FAB system divides AML into eight subtypes, M0 through to M7, based on the type of cell from which the leukemia developed and its degree of maturity. AML of types M0 to M2 may be called acute myeloblastic leukemia. Classification is done by examining the appearance of the malignant cells with light microscopy and/or by using cytogenetics to characterize any underlying chromosomal abnormalities. The subtypes have varying prognoses and responses to therapy.
When the primary site is in the skin, it is referred to as a Merkel-cell carcinoma. Extrapulmonary small-cell carcinoma localized in the lymph nodes
This is an extremely rare type of small cell, and there has been little information in the scientific community. It appears to occur in only one or more lymph nodes, and nowhere else in the body. Treatment is similar to small cell lung cancer, but survival rates are much higher than other small-cell carcinomas. Small-cell carcinoma of the prostate
Small-cell carcinoma of the prostate (SCCP) is a rare form of prostate cancer (approx. 1% of PC). Due to the fact that there is little variation in prostate specific antigen levels, SCCP is normally diagnosed at an advanced stage, after metastasis. Symptomatic metastasis of SCCP to the brain is rare, and carries a poor prognosis. Genetics
TP53 is mutated in 70 to 90% of SCLCs. RB1 and the retinoblastoma pathway are inactivated in most SCLCs. PTEN is mutated in 2 to 10%. MYC amplifications and amplification of MYC family members are found in 30% of SCLCs. Loss of heterozygocity on chromosome arm 3p is found in more than 80% of SCLCs, including the loss of FHIT. One hundred translocations have so far been reported in SCLCs (see the "Mitelman Database" and the Atlas of Genetics and Cytogenetics in Oncology and Haematology,). Diagnosis
When

Localized: the cancer is confined to the lung (aka: limited stage SCLC). Regional: the cancer has spread to lymph nodes (or glands) within the chest (between limited and extensive stage SCLC).