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Pathology Key Words for Correct Coding: Know Their Differences

Pathology Key Words for Correct Coding: Know Their Differences

Diagnosis code choice relies on a thorough understanding of the four classifications of abnormal cell growth severity.

The good news about cancer coding is that it is generally straightforward. If you can familiarize yourself with a few key pathology words, you’ll be headed in the right direction.

Stages of Cancer

Cancer is not a disease that occurs “out of nowhere.” It is typically progressive (in various stage) abnormal cell growth that is classified by severity: dysplasia, carcinoma in situ (CIS), and frank malignancy. To make a diagnosis, pathologists look at cells under a microscope to determine how abnormal the cells of a tissue are, how different they look, how fast they are multiplying, and how many cells are present.


Dysplasia is the presence of abnormal epithelial cells within tissue, which may signify a stage preceding the development of cancer. When cells lining a body structure undergo dysplastic changes, they can change shape (poikilocysotis), size (anisocytosis), or develop excessive pigmentation (hyperchromatism). There also can be an abnormal progression of immature cells dividing quickly (mitotic figures).
The premise behind cancer screening tests (e.g., Pap smears, colonoscopies, and breast biopsies) is to look at tissues under the microscope to see if there is dysplasia in the tissue. When a clinician takes a biopsy or Pap smear, they send it to pathology so the pathologist can determine if there is dysplasia (a precursor to cancer). If there is dysplasia, they monitor the patient and possibly take more tissue from the site (e.g., a cervical cone/loop electrosurgical excision procedure (LEEP), colon resection, or lumpectomy). If there is no dysplasia, the patient can wait one or several years before another screening.
Exocervix and ectocervix are interchangeable and refer to the outer surface of the cervix lined by squamous cells. Dysplasia in the cervix is usually diagnosed as low grade (mild) or high grade (moderate or severe/CIS). Severe dysplasia of the cervix is synonymous with CIS.
Dysplasia in a breast biopsy is referred to as atypia. Atypical ductal hyperplasia in a breast biopsy is carefully watched with a repeat biopsy or excision, if necessary.
ICD-10-CM coding examples:

  • Ectocervix biopsy with mild dysplasia: N87.0 Mild cervical dysplasia
  • Ectocervix biopsy with moderate dysplasia: N87.1 Moderate cervical dysplasia
  • Severe cervical dysplasia of the ectocervix: D06.1 Carcinoma in situ of exocervix
  • Focal high-grade dysplasia in a villoglandular adenoma in a rectosigmoid colon biopsy: D12.7 Benign neoplasm of rectosigmoid junction
  • Atypical ductal epithelial hyperplasia of a left breast biopsy: N60.92 Unspecified benign mammary dysplasia of left breast


CIS refers to cancerous cells that remain in their tissue of origin. These cells have not broken through the basal layer of cells or a basement membrane within a particular tissue. CIS is sometimes referred to stage 0 cancer, or pre-cancer because it has not invaded surrounding tissues. Along with CIS, there may be an invasive carcinoma nearby. In breast biopsies, the CIS can be ductal and/or lobular, and it may be seen alone or in addition to invasive carcinomas.
ICD-10-CM coding examples:

  • Squamous cell CIS of the ectocervix with extension into the endocervical glands: D06.1 and D06.0 Carcinoma in situ of endocervix
  • Adenocarcinoma in situ of the splenic flexure of the colon: D01.0 Carcinoma in situ of colon.
  • Female left breast biopsy with invasive ductal carcinoma of the upper outer quadrant, plus lobular CIS and ductal CIS: C50.412 Malignant neoplasm of upper-outer quadrant of left female breast, D05.12 Intraductal carcinoma in situ of left breast, and D05.02 Lobular carcinoma in situ of left breast.

Invasive Carcinoma

An invasive malignancy, or carcinoma, is defined as a tumor that has grown and expanded enough to break through the basal layer of cells lining the tissue and invade the surrounding normal parenchyma. This type is also called an infiltrating carcinoma.
An invasive or infiltrating carcinoma has the potential to grow into lymph channels and blood vessels, which increases the chance it will spread via lymphatics or vasculature as a metastasis. A pathologist may refer to the cells in the tumor as:

  • Well differentiated (more normal appearing), with a lower grade;
  • Moderately differentiated (mid-grade and slightly more aggressive); or
  • Poorly differentiated (high grade, bizarre cells), with the most aggressive potential.

ICD-10-CM coding examples:

  • Invasive squamous cell carcinoma of the exocervix: C53.1 Malignant neoplasm of exocervix.
  • Invasive adenocarcinoma of the sigmoid colon: C18.7 Malignant neoplasm of sigmoid colon.
  • Infiltrating lobular carcinoma in the right lower inner quadrant of a female breast with foci of lobular CIS: C50.311 Malignant neoplasm of lower-inner quadrant of right female breast and D05.01 Lobular carcinoma in situ of right female breast.


Metastasis is the spread of tumor to other parts of the body via lymphatics or blood vessels. A primary tumor can metastasize to another organ or to a regional lymph node. An example is breast cancer with metastases to axillary lymph nodes. Similarly, colon cancer can metastasize to mesenteric lymph nodes and/or the liver or other organs.
A malignant tumor has the potential to metastasize (cause a secondary tumor), and any organ may be the recipient of a secondary metastasis. Some common sites of metastases are the lungs, liver, and bones.
When treatment is directed toward the metastasis or secondary site, the metastatic site is designated as the principal/first-listed diagnosis. Code the primary malignancy with an additional code.
ICD-10-CM coding examples:

  • A pelvic lymph node excision diagnosed as a metastatic squamous cell carcinoma from an invasive ectocervical cancer: C77.5 Secondary and unspecified malignant neoplasm of intrapelvic lymph nodes and C53.1.
  • A liver biopsy with a metastatic adenocarcinoma from the ascending colon: C78.7 Secondary malignant neoplasm of liver and intrahepatic bile duct and C18.2 Malignant neoplasm of ascending colon.
  • A brain biopsy with metastatic breast cancer in a patient with a left breast invasive ductal carcinoma: C79.31 Secondary malignant neoplasm of brain and C50.912 Malignant neoplasm of unspecified site of left female breast.

Written by Maureen DeArmond, MHS, PA (ASCP)CM, CPC, has been a pathologists’ assistant for 21 years and works for Pathology Associates in Las Cruces, N.M. She earned her CPC® in 2010 and has been coding for her pathology practice for 15 years. DeArmond is a member of the El Paso, Texas, local chapter.

No Responses to “Pathology Key Words for Correct Coding: Know Their Differences”

  1. Olga says:

    This is a great article! Thank you! I do however have a question about some of the examples concerning breast cases (in particular the ones that involve invasive carcinomas and CIS of the breast). There is an Excludes 1 note under the D05 code, stating “Paget’s disease of breast and nipple (C50.-)”. Is the reason you can code D05.01 and C50.311 together, as it appears in one of the examples in the article, because the patient does not have Paget’s disease documented? Are we then to go by the specific CONDITIONS listed in the Excludes 1 notes and not merely by the CODES that are listed in the parenthesis?
    Thank you very much!