Cell identity, state, and subtype
Three questions often appear in the same paragraph: what kind of cell is this, what is it doing, and how is the cancer classified? They describe different things.
Identity and state
We can describe a cell’s family and current activity separately. Receptor tests and RNA classifiers also answer different questions.
| Term | Meaning | What the label alone cannot establish |
|---|---|---|
| Malignant | Cancerous | A specific treatment sensitivity |
| Lineage | A cell family and its developmental relationships | The exact ancestral cell of an individual tumor |
| Progenitor | A less mature cell able to give rise to more specialized descendants | That a progenitor-like cancer cell is a normal stem cell |
| Differentiation | Becoming more specialized in structure or function | How aggressive a cancer is from one RNA label |
| Cell state / program | A coordinated pattern of activity, such as proliferation or hormone response | A permanent identity; states can change |
| Marker | A feature used to help identify or characterize cells | A unique identity from one gene |
| Cluster | A computational group of similar measured profiles | A proven cell type or clone |
Normal breast atlases distinguish luminal hormone-responsive, luminal secretory, and basal/myoepithelial populations, with further states within them. Luminal-progenitor-like means resemblance to a less mature luminal program. It is an expression comparison, not a direct observation of the tumor's birth. Human breast atlas
Why “basal” and “luminal” are confusing
Basal can refer to the outer epithelial layer of normal breast structures. Basal-like can also name a tumor expression subtype. Luminal can describe normal lining cells, while luminal A/B names tumor expression classes commonly associated with hormone-receptor-positive biology.
TNBC is a clinical receptor category: estrogen receptor, progesterone receptor, and HER2 testing are negative under their clinical criteria. PAM50 is a classifier based on expression of 50 genes. NCI: clinical receptor classification A lineage-like RNA state is another description again. A basal-like tumor can resemble luminal progenitors; primary research in BRCA1 carriers illustrates this distinction. It does not establish the origin of every TNBC. Lim et al., Nature Medicine
The October 4 review's luminal-progenitor-like result therefore does not reclassify Diana's clinical TNBC as hormone-receptor-positive cancer.
Epithelial and mesenchymal features
Mesenchymal describes connective-tissue-associated features. Epithelial–mesenchymal transition (EMT) describes changes in adhesion, organization, and motility programs; cells can have mixed features. E-cadherin participates in cell adhesion. Keratins are structural proteins often used as epithelial markers. Vimentin is associated with mesenchymal features but also occurs in normal supporting cells.
EMT definitions and intermediate states provide the framework for describing those changes.
A high vimentin signal in a whole biopsy cannot tell us whether cancer cells adopted an EMT-like program or whether the sample contained many stromal cells. The October 4 review uses cell-specific comparisons to address this mixture problem; one marker still does not prove invasion, metastatic behavior, or drug resistance. Report findings and qualifications
Say it in your own words
“TNBC describes the clinical receptor tests. Luminal-progenitor-like describes an RNA pattern in the cancer cells. Those labels answer different questions and can coexist.”
Check yourself: Do two nuclei in one RNA cluster necessarily belong to the same genetic clone? No. Similar activity is different from shared acquired DNA changes. Next: reading RNA counts.