Understanding Your Pathology Report: Lung Cancer

When your lung was biopsied, the samples taken were studied under the microscope by a specialized doctor with many years of training called a pathologist. The pathologist sends your doctor a report that gives a diagnosis for each sample taken. Information in this report will be used to help manage your care. The questions and answers that follow are meant to help you understand medical language you might find in the pathology report you received for your biopsy.

The information that would be in a pathology report based on having all or part of your lung removed (resected) as a treatment for lung cancer is not covered here.

What is the normal structure of the lung?

When you breathe in, air enters through your mouth or nose and goes into your lungs through the trachea (windpipe). The trachea divides into 2 tubes called the bronchi (singular, bronchus), which divide into smaller branches called bronchioles. At the end of the bronchioles are tiny air sacs known as alveoli or acini.

Many tiny blood vessels run through the alveoli. They allow oxygen from the air that you breathe in to be absorbed into your blood and pass carbon dioxide from the body into the alveoli. This is expelled from the body when you breathe out. Taking in oxygen and getting rid of carbon dioxide are your lungs' main functions.

What is carcinoma?

Carcinoma is a type of cancer that starts in the cells that line organs. In the lung, carcinomas can start in the cells that line the bronchi, bronchioles, and alveoli. Carcinoma is the most common kind of lung cancer. In fact, when someone says they have lung cancer, they usually mean that they have a carcinoma.

What does infiltrating or invasive mean?

Carcinomas can start in the cells that line the bronchi, bronchioles, or alveoli. If the carcinoma cells are only in the top layer of cells lining these structures, it is called in-situ carcinoma. This is considered a pre-cancer.

When carcinoma cells grow into the deeper layers of the lung, it is called invasive or infiltrating carcinoma. At this point the cancer cells can spread (metastasize) outside of the lung to lymph nodes and other parts of your body. Invasive carcinomas are considered true cancers and not pre-cancers.

What does it mean if my carcinoma is called squamous carcinoma or squamous cell carcinoma?

Carcinomas are named based on how the cells look under the microscope. Squamous carcinoma or squamous cell carcinoma is the name of a type of lung cancer where the cells resemble the flat cells (called squamous cells) that line the airways. It is a common type of lung cancer in the United States.

What does it mean if my carcinoma is called adenocarcinoma?

Carcinomas are named based on how the cells look under the microscope. Adenocarcinoma is a type of carcinoma where the cells resemble gland cells, such as the glands that secrete mucus in the lungs. It is the most common type of lung cancer in the United States.

What does it mean if the following terms are used to describe the adenocarcinoma: papillary, bronchioloalveolar, mucinous, micropapillary, or solid?

These terms describe different types of lung adenocarcinoma based on how the cells look and are arranged under the microscope (called growth patterns). Some tumors look basically the same throughout the tumor, and some can look different in different areas of the tumor. Some growth patterns have a better prognosis (outlook) than others. Still, since some tumors can have a mixture of patterns, we can’t always tell all the types contained in a tumor based on a biopsy which sampled only a small part of the tumor. To know what types a tumor contains, the entire tumor must be removed.

What does it mean if my carcinoma is called large cell carcinoma or large cell undifferentiated carcinoma?

In some cases, the cancer does not look like squamous cell carcinoma, adenocarcinoma, small cell carcinoma (see below), or any of the other more rare variants of lung cancer under a microscope. These cancers are called undifferentiated large cell carcinoma (or undifferentiated non-small cell carcinoma). These tumors have a better prognosis than small cell carcinoma and in general they are treated the same way as adenocarcinoma of the lung.

What does it mean if my carcinoma is called small cell carcinoma, oat cell carcinoma, or small cell undifferentiated carcinoma?

Small cell carcinoma, oat cell carcinoma, or small cell undifferentiated carcinoma is a special type of lung cancer that tends to grow and spread quickly. Since it has often spread outside the lung at the time it is diagnosed, it is rarely treated with surgery. It is most often treated with chemotherapy, which might be combined with radiation. The chemotherapy used is different from what is used for other types of lung cancers.

What does it mean if my carcinoma is well differentiated, moderately differentiated, or poorly differentiated?

These terms are used to indicate how aggressive your carcinoma is likely to be (how fast it is likely to grow and spread). They are assigned by a pathologist based on how the cancer cells look under the microscope. Well-differentiated carcinomas tend to grow more slowly, and have a better prognosis (outlook). Poorly differentiated carcinomas are the most aggressive tumors, with a worse prognosis, and moderately differentiated carcinomas have an intermediate (in-between) prognosis.

What does it mean if my report says typical carcinoid or atypical carcinoid tumor?

Carcinoid tumors are a special type of tumor. They start from cells of the diffuse neuroendocrine system. This system is made up of cells that are like nerve cells in certain ways and like hormone-making endocrine cells in other ways. These cells do not form an actual organ like the adrenal or thyroid glands. Instead, they are scattered throughout the body in organs like the lungs, stomach, and intestines.

Like most cells in your body, lung neuroendocrine cells sometimes go through certain changes that cause them to grow too much and form tumors. These are known as neuroendocrine tumors or neuroendocrine cancers. Neuroendocrine cells in other parts of the body can also form tumors and cancers. There are 4 types of neuroendocrine lung tumors: small cell lung carcinoma, large cell neuroendocrine carcinoma, atypical carcinoid tumor, and typical carcinoid tumor.

Typical carcinoid tumors of the lungs are not linked to smoking. They tend to be slow growing, and only rarely spread outside the lungs.

Atypical carcinoid tumors grow a little faster and are somewhat more likely to spread to other organs. Seen under a microscope, they have more cells in the process of dividing and look more like a fast-growing tumor. They are much less common than typical carcinoids. Some of the features of an atypical carcinoid that may be mentioned in your report include: mitotic figures or mitoses (an indication of how fast the tumor is growing) and necrosis (when areas of the tumor are dead).

Some carcinoid tumors can release hormone-like substances into the bloodstream. Lung carcinoids do this far less often than carcinoid tumors that start in the intestines.

What is vascular, angiolymphatic or lymphovascular invasion? What if my report mentions D2-40 (podoplanin) or CD34?

Tumors can grow into small vessels (blood vessels and/or lymphatic vessels). When this is seen under the microscope it is called vascular, angiolymphatic or lymphovascular invasion. If cancer is present in vessels it means there is a higher chance that the cancer has spread outside the lung, although this does not always occur.

D2-40 and CD34 are special tests the pathologist may use to help identify vascular, lymphovascular or angiolymphatic invasion. These tests are not necessary for every patient. If your report does not mention this type of invasion, it means that it is not present. How this finding affects your treatment is best discussed with your doctor.

What is the significance of the reported size of the tumor?

If the entire tumor is removed, the pathologist will measure it by just looking at it (called the gross examination), or, if it is very small, measure it under the microscope. Often, what is reported is how big it is across in the area where the tumor is the largest. This is called the greatest dimension of the tumor, as in “the tumor measured 2 cm in greatest dimension.” In general, smaller tumors have a better prognosis (outlook).

A biopsy of a tumor or cancer under bronchoscopy or with a needle only samples a part of the tumor, so the size of the tumor is not reported for these types of biopsies.

What is the significance of the stage of the cancer?

The stage of the tumor is a measurement of the extent of cancer and its spread. To know the stage of a lung cancer, you need information on the size of the tumor in the lung and if the cancer is growing into any nearby organs or structures. You also need to know if the cancer has spread to any lymph nodes or distant sites.

Each of these pieces of information is represented by a letter, where T stands for tumor, N for lymph nodes, and M for distant metastasis (spread). The T, N, and M stages are combined to create an overall stage, which is given a number of I to IV, with a higher number meaning larger extent or spread of disease.

When this information is obtained by removing the tumor and nearby lymph nodes at surgery, a lower-case letter “p” is put before the T and N.

So, in your pathology report, pT will be followed by numbers and letters based on the size of the tumor and some other information about it — the larger the number, the more advanced the cancer. pN followed by numbers and letters is based on the extent of spread to lymph nodes that may have been removed at the same time as the lung tumor. The pathologist cannot determine whether there is spread to distant sites (i.e., liver, bone) based on surgery to remove a lung tumor and nearby lymph nodes, so pM will not be on the report. The M category is often based on the results of imaging studies, such as CT scans, MRIs, and bone scans, sometimes along with a biopsy of an area of suspected cancer spread.

This staging system is used for many types of lung cancer, such as adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. These types of lung cancer are often grouped together as non-small cell lung cancer. This staging system also can be used to stage carcinoid tumors, but is not often used for small cell carcinomas of the lung.

In order to report the T and N stages on a pathology report, the pathologist needs to have the entire tumor and nearby lymph nodes to evaluate. This is most often from surgery aimed at curing the cancer, not just a biopsy. Because a needle (or bronchoscopic) biopsy only samples part of the cancer, the cancer’s stage is not reported for these types of biopsy.

Detailed information on staging for non-small cell lung cancer can be found in our document, Lung Cancer—Non-Small Cell in the section “How is non-small cell lung cancer staged?” and at the American Joint Committee on Cancer web-site: www.cancerstaging.org, Staging Resources. Discuss how the stage of your tumor will affect your treatment with your physician.

What does it mean if in addition to a diagnosis of cancer, my report also says atypical adenomatous hyperplasia or squamous dysplasia or squamous cell carcinoma in-situ?

All of these are terms for pre-cancers that can be found in the lung. They are sometimes found near invasive cancer. If they are found on needle biopsy in addition to invasive cancer, it isn’t really important. If they are found in a specimen from surgery to remove the entire tumor, they may be important if they are found at or near a margin (discussed in a previous question).

What if my report mentions margins or ink?

When an entire tumor or abnormal area is removed, the pathologist coats the outer edges, or margins, of the tissue with ink, sometimes with different colored ink on different sides. If a cancer (and/or pre-cancer) is found, the pathologist can then tell if it goes up to the ink (and the edges of tissue removed). If it does, it may mean that some cancer (or pre-cancer) has been left behind. Sometimes this is not a concern because the surgeon removed other tissue in that area. Still, if some cancer (or pre-cancer) has been left behind, you might need more treatment, such as radiation or more surgery You should talk with your doctor about the best approach for you if cancer (or pre-cancer) is found at the margins.

What does it mean if my report mentions special studies such as p63, cytokeratin 5/6 (CK5/6), and TTF-1?

p63, cytokeratin 5/6, and TTF-1 are special tests that the pathologist sometimes uses to help tell adenocarcinoma from squamous cell carcinoma.

What does it mean if my report mentions special studies such as CK7 (cytokeratin 7), CK20, CDX2, gross cystic duct fluid protein (GCDFP), mammaglobin, estrogen receptor (ER), progesterone receptor (PR), along with TTF-1 or PE-10?

These tests are sometimes used to help determine if a cancer in the lung started there (is a primary lung cancer) or spread there from somewhere else (is a metastasis). Not all patients need these tests, so if your report does not mention them, it doesn’t mean there is a problem or a question about your diagnosis.

What does it mean if my report mentions special studies such as CD56, chromogranin, or synaptophysin?

These tests are sometimes used to help see if a lung cancer is a small cell carcinoma. They can also be helpful in diagnosing carcinoid or atypical carcinoid tumor.

What does it mean if my report mentions special studies such as mesothelin, D2-40 (podoplanin), calretinin, CEA, cytokeratin (CK) 5/6, HBME-1, Ber-EP4, TTF-1, CD15 (LeuM1), WT-1?

These tests are sometimes used to help see if a tumor in the lung is mesothelioma or an adenocarcinoma of the lung.

What if my report mentions EGFR, K-ras, or ALK?

These are tests done for specific gene changes in the cancer cells that might affect how they are best treated. These tests are done on adenocarcinomas, because these lung cancers are most often affected by these changes. How the results of your tests will affect your treatment is best discussed with your physician.

What does it mean if my cancer is called malignant mesothelioma?

These are not technically lung cancers, because they don’t develop from cells in the lung. They come from the tissue coating the outside of the lung called pleura. They are not carcinomas. Mesotheliomas are often described based on how they look under the microscope with terms like epithelial, spindled, sarcomatoid, or mixed epithelial and spindle cell features. Mesotheliomas may be linked to exposure to asbestos. They often have a poor prognosis (outlook).

What does it mean if my report says that there is metastatic carcinoma to the lung?

Cancers from other organs often spread to the lung. Spread of cancers is called metastasis, and a carcinoma that spread to the lung is called metastatic carcinoma to the lung. Cancers that spread to the lung are still named after where they started — they are not considered lung cancers. For example, if an adenocarcinoma of the colon (i.e., colon cancer) spreads (metastasizes) to the lung it is still a colon cancer, and not a lung cancer. This is important because chemotherapy for an adenocarcinoma of the lung is different from that used for adenocarcinoma of the colon.

What does it mean if my report also has any of the following terms: scarring, emphysema, emphysematous changes, or inflammation?

All of these are terms for non-cancerous changes that the pathologist sees under the microscope and usually are not important when seen on a biopsy or resection which also contains cancer.

What if my report mentions any of the following: granulomas, methenamine silver (GMS), acid fast bacilli (AFB), or Periodic Acid Schiff (PAS).

Granulomas are structures seen under the microscope that are often, although not always, caused by certain types of infections. Sometimes, the organisms causing the infection can be seen with special stains (i.e., GMS, stains for AFB, and PAS) that the pathologist can apply to the microscopic slides. Most granulomas are caused by infections, but other things can cause them, too, such as a disease called sarcoidosis, allergic reactions, and dust-induced lung disease (pneumoconiosis).

This series of Frequently Asked Questions (FAQs) was developed by the association of Directors of Anatomic and Surgical Pathology to help patients and their families better understand what their pathology report means. These FAQs have been endorsed by the College of American Pathologists (CAP) and reviewed by the American Cancer Society.

Learn more about the FAQ Initiative

Last Medical Review: October 14, 2014 Last Revised: October 14, 2014

Copyright 2011 Association of Directors of Anatomic and Surgical Pathology, adapted with permission by the American Cancer Society.