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The International Classification of Diseases for Oncology (ICD-O) is a collaborative undertaking of the International Agency for Research on Cancer (IARC) and the National Cancer Institute (NCI) in the U.S., under the aegis of the World Health Organization (WHO). The first edition of the ICD-O (published in 1976) is an extension of the second chapter (“Neoplasms”) of the ninth revision of the International Classification of Diseases (ICD-9) and, in addition to the ICD-9 codes (which describe anatomic sites of tumors), also allows the coding of histology. The second edition of the ICD-O (published in 1990)1 similarly extends the second chapter of the 10th revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-10).

The ICD-O codes tumors based on topography (anatomic location), morphology (histology), and behavior (malignant, benign, in situ, of uncertain behavior, or metastatic) but not staging. The topography codes are listed as C00.0 to C80.9. The morphology codes (M) in the second edition were modified in particular for non-Hodgkin lymphoma to accommodate the Working Formulation for this group of diseases. The morphology codes range from 8000/0 to 9989/1, in which the first 4 digits of the code indicate the specific histology and the 5th digit (after the slash) is the behavior code. A separate 1-digit code identifies histologic grading (differentiation) and also is used for T cell and B cell categorization in leukemias and lymphomas. Accordingly, the full description of a neoplasm in the ICD-O is a 10-item alpha numeric: 4 for topography, 4 for morphology, 1 for behavior, and 1 for histologic grade. As an example, acute lymphoblastic leukemia of B precursor type is coded as C42.1 9821/3 6.

Although the ICD-O system generally is applicable to cancers diagnosed in childhood, it is recognized that morphology takes precedence over topography in classifying neoplasms occurring in children. For example, rhabdomyosarcoma occurs nearly everywhere in the body. Furthermore, for the purposes of international comparison and the facilitation of analysis, an aggregation of diagnostic codes is valuable. To this end, a classification scheme was developed for widespread use2 based on the system used at the Manchester (U.K.) Children's Tumour Registry. Included in the considerations at that time were the desirability of having a standard framework while allowing for the flexibility of subdivisions within a small number of main groups, and the allocation of the maximum number of codes to specific categories so that the number of malignancies grouped as “other” is minimized.

That classification scheme was updated in 1996 while maintaining the framework of 12 main diagnostic groups.3 The major modifications were the exclusion of Langerhans cell histiocytoses, a subgroup of germ cell tumors for those occurring in the central nervous system (CNS), a subgroup for Kaposi sarcoma within soft tissue sarcomas, a subgroup for skin carcinoma within epithelial neoplasms, and the assignment of the majority of “other specified” and “unspecified” neoplasms to subgroups within the main diagnostic groups.

As useful as the International Classification of Childhood Cancer (ICCC) has proven to be, even when applied to the malignant diseases afflicting adolescents,4 it is well appreciated that the distribution of neoplasms affecting the adolescent and young adult (AYA) age group (commonly defined as those ages 15–29 yrs) is very different from that found in early childhood. The embryonal tumors so characteristic of the latter group of patients are seldom encountered among the former group, whereas carcinomas assume much greater importance in the AYA group. An example of the limitations of the ICCC as applied to cancers diagnosed in AYA patients is illustrated in Tables 1–3 using population-based data from the Province of Ontario, Canada. The proportion of cases in categories XI, XII, and “Not classified” increases progressively in the successive age quintiles of 15–19 years, 20–24 years, and 25–29 years from < 20% to nearly 50% (Table 1). The comparable proportion in patients ages birth–14 years is approximately 5%. In the AYA population, these ICCC categories are comprised mainly of squamous cell carcinoma, adenocarcinoma, and melanoma (Table 2). Although the thyroid is the most common site overall (accounting for greater than 33% of tumors diagnosed in males and 50% of tumors diagnosed in females in the 15–19 yrs age group), there is a notable progressive increase in tumors of the breast and uterine cervix across the quintiles (Table 3).

Table 1. International Classification of Childhood Cancer. Province of Ontario, Canada, 1991-2000 (Incident Cases among Adolescents and Young Adults, Both Genders Combined)
  Age range
  15–19 yrs20–24 yrs25–29 yrs
ICCC categoryNo.%No.%No.%
  1. ICCC: International Classification of Childhood Cancer; CNS: central nervous system; SNS: sympathetic nervous system.

  2. Adapted from the Ontario Cancer Registry Incidence File, Cancer Care Ontario (1979-2004) (OCRIS 03/2005). Software used was Surveillance Research Program of the U.S. National Cancer Institute (SEER*Stat software, version 5.2.2; National Cancer Institute, Bethesda, MD).

ILeukemia17111.241616.372044.53
IILymphoma45529.8963425.0781718.14
IIICNS tumors1479.661766.962746.08
IVSNS tumors50.3330.1290.20
VRetinoblastoma00.0010.0410.02
VIRenal tumors80.53160.63440.98
VIIHepatic tumors80.53100.40180.40
VIIIBone tumors1066.96652.57681.51
IXSoft tissue sarcomas1046.83973.841763.91
XGerm cell tumors21614.1947818.9070315.61
XICarcinomas27918.3378731.12196943.73
XIIOther/unspecified tumors201.31913.602074.60
 Not classified30.20100.40130.29
 Invalid values00.0000.0000.00
        
 Total1522100.002529100.004503100.00
Table 2. Classification of Cancer by Morphology, ICCC Categories XI, XII, and Not Classified. Province of Ontario, Canada, 1991-2000 (Incident Cases among Adolescents and Young Adults, Both Genders Combined)
Morphology groupAge range
15–19 yrs20–24 yrs25–29 yrs
No.%No.%No.%
  1. ICCC: International Classification of Childhood Cancer; NOS: not otherwise specified.

  2. Adapted from the Ontario Cancer Registry Incidence File, Cancer Care Ontario (1979-2004) (OCRIS 03/2005). Software used was Surveillance Research Program of the U.S. National Cancer Institute (SEER*Stat software, version 5.2.2; National Cancer Institute, Bethesda, MD).

Neoplasm, NOS165.30829.231918.73
Carcinoma, NOS92.98171.91492.24
Squamous cell10233.7724327.3660327.55
Basal cell00.0000.0020.09
Transitional cell30.9991.01311.42
Adenocarcinoma6622.1919822.3043619.92
Cystic/mucinous/serous10.33101.13572.60
Ductal/lobular72.32455.0726712.20
Other epithelial247.95262.93683.11
Melanomas6722.1923926.9146121.06
Sarcomas30.99121.35170.78
Leukemias10.3300.0000.00
Others20.6670.7970.32
       
Total302100.00888100.002189100.00
Table 3. Classification of Cancer by Primary Site, ICCC Categories XI, XII, and Not Classified. Province of Ontario, Canada, 1991-2000 (Incident Cases among Adolescents and Young Adults, Both Genders Combined)
Primary siteaAge range
15–19 yrs20–24 yrs25–29 yrs
No.%No.%No.%
  • ICCC: International Classification of Childhood Cancer; CNS: central nervous system.

  • a

    Most prevalent sites only.

  • Adapted from the Ontario Cancer Registry Incidence File, Cancer Care Ontario (1979-2004) (OCRIS 03/2005). Software used was Surveillance Research Program of the U.S. National Cancer Institute (SEER*Stat software, version 5.2.2; National Cancer Institute, Bethesda, MD).

Oral cavity/pharynx4115.19506.111055.22
Esophagus00.0020.2450.25
Stomach20.74101.22261.29
Colon and rectum82.96425.131125.57
Pancreas10.37121.47120.60
Lung/bronchus31.11273.30733.63
Skin melanoma6323.3323228.3644322.02
Breast72.59384.6528214.02
Cervix62.22617.4632316.05
Uterine corpus00.0040.49180.89
Ovary00.0010.1220.10
Prostate10.3720.2460.30
Testis00.0010.1200.00
Urinary bladder31.01192.32381.89
Kidney/renal pelvis00.0000.0000.00
Brain/other CNS00.0020.2400.00
Thyroid13550.0031538.5156728.18
       
Totala270100.00818100.002012100.00

Consequently, a classification scheme has been proposed that is tailored to the particular circumstances of AYA patients with cancer (Table 4).5 Again, this scheme is based on the ICD-O. Ten main diagnostic groups are defined, all but 1 of which (No. 10, “unspecified”) have subgroups of which nearly half are subdivided further. The classic embryonal tumors that typically occur in young children are largely grouped together. In the proposed classification, malignant germ cell tumors, which are more prevalent among AYA patients than children, form a separate group. Likewise, carcinomas are addressed in more detail. Additional innovations include the grouping of all Ewing sarcomas and related tumors together, and a more detailed classification of malignant CNS tumors. In situ tumors and neoplasms of uncertain behavior occurring outside the CNS are excluded.

Table 4. Classification of Cancers in Adolescents and Young Adultsa
  ICD-02
Diagnostic groupMorphology codeTopography code restrictions
  • ICD-O2: International Classification of Diseases for Oncology, 2nd edition; NOS: not otherwise specified; NHL: non-Hodgkin lymphoma; CNS: central nervous system; PNET: primitive neuroectodermal tumor; NEC: not elsewhere classified.

  • a

    Unless otherwise specified, only tumors with behavior codes of 3 or more were included.

  • b

    Included peripheral neuroectodermal tumors.

  • c

    Includes Ewing tumor and peripheral neuroectodermal tumors coded to extraskeletal sites.

  • d

    Includes malignant fibrous histiocytoma of the bone.

1.LEUKEMIAS  
1.1Acute lymphoid leukemia9821, 9825, 9826, 9827 
1.2Acute myeloid leukemia9840, 9861, 9866, 9891, 9910, 9942 
1.3Chronic myeloid leukemia9863 
1.4Other and unspecified leukemias  
1.4.1Other lymphoid leukemia and lymphoid leukaemia, NOS9820,9822,9823,9824 
1.4.2Other myeloid leukemia and myeloid leukaemia, NOS9860,9862,9864,9865 
1.4.3Other specified leukemias9810, 9830, 9841, 9842, 9850, 9867, 9868, 9870, 9880, 9890, 9892, 9893, 9894, 9900, 9920, 9930, 9931, 9932, 9940, 9941 
1.4.4Unspecified leukemias9800-9804 
2.1LYMPHOMAS  
2.1.1NHL, specified subtype9593-9649, 9670-9714, 9723 
2.1.2Unspecified NHL9590, 9591, 9592 
2.2Hodgkin disease:  
2.2.1Hodgkin disease, specified subtype9652-9667 
2.2.2Hodgkin disease, NOS9650 
3.CNS AND OTHER INTRACRANIAL AND INTRASPINAL NEOPLASMS (tumors with any behavior code were included)  
3.1Astrocytoma  
3.1.1Specified low-grade astrocytic tumors9380C72.3
  9410-9424None
3.1.2Glioblastoma and anaplastic astrocytoma9401, 9440-9442, 9481None
3.1.3Astrocytoma, NOS9400None
3.2Other glioma9380Except C72.3
  9381-9384, 9430, 9443-9460None
3.3Ependymoma9391-9394None
3.4Medulloblastoma and other PNET  
3.4.1Medulloblastoma9470-9473C71.6
3.4.2Supratentorial PNET9470-9473Except C71.6
3.5Other specified intracranial and intraspinal neoplasms8140, 8270-8281, 8300, 9161, 9350, 9360-9362, 9390, 9480, 9505, 9530-9539, 9540-9570Except C70.0–C72.9 C75.1, C75.3
3.6Unspecified intracranial and intraspinal neoplasms  
3.6.1Unspecified malignant intracranial and intraspinal neoplasms (behavior code of 3 or more)8000-8004, 9990C70.0–C72.9, C75.1, C75.3
3.6.2Unspecified benign and borderline intracranial and intraspinal neoplasms (behavior code of less than 3)8000-8004, 9990C70.0–C72.9, C75.1, C75.3
4.OSSEOUS AND CHONDROMATOUS NEOPLASMS, EWING TUMOR, AND OTHER NEOPLASMS OF BONE  
4.1Osteosarcoma9180-9190None
4.2Chondrosarcoma9220-9240None
4.3Ewing tumor9260, 9364bNonec
4.4Other specified and unspecified bone tumors  
4.4.1Other specified bone tumors8812, 9250, 9261, 9370None
4.4.2Unspecified bone tumors8000-8004, 8800, 8801, 8803C40.0–C41.9
5.SOFT TISSUE SARCOMAS  
5.1Fibromatous neoplasms8810, 8811, 8813-8833None
5.2Rhabdomyosarcoma8900-8920, 8991None
5.3Other specified soft tissue sarcoma:  
5.3.1Specified8804, 8840-8896, 8990, 9040-9044, 9120-9150, 9170, 9251, 9561,9581, 9580Noned
  9540,9560Except C70.0–C72.9, C75.1, C75.3
5.3.2Unspecified8800-8803Except C40.0–C41.9
6.GERM CELL AND TROPHOBLASTIC NEOPLASMS  
6.1Germ cell and trophoblastic neoplasms of gonads.9060-9102C56.9, C62.0–C62.9
6.2Germ cell and trophoblastic neoplasms of nongonadal sites  
6.2.1Intracranial (tumors with any behavior code are included)9060-9102C70.0–C72.9, C75.1, C75.3
6.2.2Other nongonadal sites9060-9102Any site except C56.9, C62.0–C62.9, C70.0–C72.9, C75.1, C75.3
7.MELANOMA AND SKIN CARCINOMAS  
7.1Melanoma8720-8780None
7.2Skin carcinomas8010-8580C44.0–C44.9
8.CARCINOMAS  
8.1Thyroid carcinoma8010-8580C73.9
8.2Other carcinoma of head and neck  
8.2.1Nasopharyngeal carcinoma8010-8580C11.0–C11.9
8.2.2Other sites in lip, oral cavity and pharynx.8010-8580C00.0–C10.9, C12.0–C14.8
8.2.3Nasal cavity, middle ear, sinuses, larynx, and other and ill-defined head and neck8010-8580C30.0–C32.9, C76.0
8.3Carcinoma of trachea, bronchus, and lung8010-8580C33.0–C34.9
8.4Carcinoma of breast8010-8580C50.0–C50.9
8.5Carcinoma of genitourinary tract:  
8.5.1Carcinoma of kidney8010-8580C64.9
8.5.2Carcinoma of bladder8010-8580C67.0–C67.9
8.5.3Carcinoma of gonads8010-8580C56.0, C62.0–C62.9
8.5.4Carcinoma of cervix and uterus8010-8580C53.0–C55.9
8.5.5Carcinoma of other and ill-defined sites in genitourinary tract8010-8580C51.0–C52.9, C57.0–C57.9, C60.0–C61.9, C63.0–C63.9, C65.9, C66.9, C68.0–C68.9
8.6Carcinoma of gastrointestinal tract  
8.6.1Carcinoma of colon and rectum8010-8580C18.0–C21.8
8.6.2Carcinoma of stomach8010-8580C16.0–C16.9
8.6.3Carcinoma of liver and intrahepatic bile ducts8010-8580C22.0, C22.1
8.6.4Carcinoma of pancreas8010-8580C25.0–C25.9
8.6.5Carcinoma of other and ill-defined sites in gastrointestinal tract8010-8580C15.0–C15.9, C17.0–C17.9, C23.0–C24.9, C26.0–C26.9
8.7Carcinoma of other and ill-defined sites, NEC  
8.7.1Adrenocortical carcinoma8010-8580C74.0–C74.9
8.7.2Carcinoma of other and ill-defined sites, NEC8010-8580Any other C codes including C58.9 except C70.0–C72.9, C75.1, C75.3
9.MISCELLANEOUS SPECIFIED NEOPLASMS, NEC  
9.1Other pediatric and embryonal tumors, NEC:  
9.1.1Wilms tumor8960-8962 
9.1.2Neuroblastoma9490, 9500 
9.1.3Other pediatric and embryonal tumors, NEC8963, 8964, 8970-8972, 8981, 9501-9523 
9.2Other specified neoplasms, NEC  
9.2.1Paraganglioma and glomus tumors8680-8710 
9.2.2Other specified gonadal tumors8600-8650, 9000 
9.2.3Myeloma, mast cell tumors, and miscellaneous lymphoreticular neoplasms, NEC9720-9764 
9.2.4Other specified neoplasms, NEC8930-8951, 8980, 9020, 9050-9053, 9110, 9270-9330 
10.UNSPECIFIED MALIGNANT NEOPLASMS, NEC  
10.Unspecified malignant neoplasms, NEC8000-8004,9990Any site except: C40.0–C41.9, C70.0–C72.9, C75.1, C75.3

Algorithms for selecting tumor groups according to this scheme are provided at URL: http://www.biomed2.man.ac.uk/crcpfcrg/CRUKPFCRG/PFCRG.htm [accessed February 2, 2006]. The scheme was formulated on the basis of tabulations of the frequencies of ICD-O histology codes among a national dataset of 25,000 cases of cancer diagnosed among young people in England who were ages 15–24 years. It provides a much more balanced vehicle for the presentation of data regarding cancers occurring in the AYA age group compared with the ICCC. ICCC Groups IV, V, VI, and VII, which mainly comprise the non-CNS embryonal tumors of childhood, are irrelevant in patients within the AYA age range. Conversely, carcinomas of the head and neck, breast, genitourinary system, colon, and rectum, and other aerodigestive tract carcinomas that are significant in young adults, are not dealt with adequately in the ICCC but form specified subgroups and are discussed in detail in the AYA scheme. A standardized system for the analysis and presentation of data regarding malignancies diagnosed in the AYA age group that addresses the major disease types occurring in this age group will facilitate international comparisons of incidence and subsequently the generation of hypotheses concerning the etiology of such tumors.

Versions of this classification are available in both the first and second editions of the ICD-O.5 A third edition of the ICD-O (ICD-O3) has been published.6 This new edition is not yet widely in use but is in the process of being adopted by cancer registries internationally. The ICD-O3 includes many new codes of relevance to tumors occurring in the AYA population. The most extensive revisions are with regard to leukemias and lymphomas. The codes incorporate the WHO classification,7, 8 which superceded the Revised European–American Lymphoma (REAL) classification for lymphomas9 and the French–American–British (FAB) classification for leukemias.10 The ICCC recently was adapted for use with the ICD-03.11 A revised version of the AYA classification scheme based on the ICD-O3 will be made available during 2006.

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