Histopathological growth patterns of liver metastasis: updated consensus guidelines for pattern scoring, perspectives and recent mechanistic insights

Abstract

The first consensus guidelines for scoring the histopathological growth patterns (HGPs) of liver metastases were established in 2017. Since then, numerous studies have applied these guidelines, have further substantiated the potential clinical value of the HGPs in patients with liver metastases from various tumour types and are starting to shed light on the biology of the distinct HGPs. In the present guidelines, we give an overview of these studies, discuss novel strategies for predicting the HGPs of liver metastases, such as deep-learning algorithms for whole-slide histopathology images and medical imaging, and highlight liver metastasis animal models that exhibit features of the different HGPs. Based on a pooled analysis of large cohorts of patients with liver-metastatic colorectal cancer, we propose a new cut-off to categorise patients according to the HGPs. An up-to-date standard method for HGP assessment within liver metastases is also presented with the aim of incorporating HGPs into the decision-making processes surrounding the treatment of patients with liver-metastatic cancer. Finally, we propose hypotheses on the cellular and molecular mechanisms that drive the biology of the different HGPs, opening some exciting preclinical and clinical research perspectives.

Fig. 1. The histopathological growth patterns of liver metastases (H&E images).

a Low-magnification image of a CRC liver metastasis with a desmoplastic HGP. b, c Higher magnification of the tumour–liver interface of CRC liver metastases with a desmoplastic HGP. The blue double-headed arrow indicates the desmoplastic rim that separates the carcinoma from the liver parenchyma. The green arrowheads indicate the immune cell infiltrate which is typically located at the transition between the desmoplastic rim and the liver parenchyma. The tumours show glandular differentiation and cell detritus in the lumina of these glandular structures, reminiscent of the histology of a primary CRC (white arrowheads). d Low-magnification image of a CRC liver metastasis with a replacement HGP. The green arrowheads indicate the tumour–liver interface. There is no glandular differentiation: cancer cells from solid nests and trabeculae. e, f Higher magnification of the tumour–liver interface of CRC liver metastases with a replacement HGP. The green arrowheads indicate contact between cancer cells and hepatocytes. In (e), cancer cells form cell plates that are in continuity with the liver cell plates. A co-opted sinusoidal blood vessel is marked by the blue arrowheads. In (f), the liver cell plates are pushed aside but cancer cells are still in contact with hepatocytes while invading into these liver cell plates (green arrowheads). g Low-magnification image of a CRC liver metastasis with a pushing HGP. h On higher magnification, a sharp tumour–liver interface is noticed without desmoplastic rim and without cancer cells invading into the liver parenchyma. Often metastases with a pushing HGP produce mucin, as shown in this example. i Lobular breast carcinoma liver metastasis with a sinusoidal HGP (autopsy case). Cancer cells are located within the lumen of sinusoidal blood vessels (green asterisks), in between liver cell plates (blue asterisks). Red blood cells are intermingled with the cancer cells (blue arrowheads). j Low-magnification image of intrabiliary tumour growth (CRC) in a portal tract. The structures constituting a portal tract are present: artery branches (A), vein branch (V), nerve bundle (N) and branches of the bile duct (B), in this case filled with cancer cells. k Higher magnification of the left bile duct branch of image J. The normal bile duct epithelium (blue arrowheads) is still present but is replaced by cancer tissue that fills the lumen of the bile duct branch.

Fig. 2. Survival of patients with colorectal liver metastases according to different cut-off values for histopathological growth patterns.

Kaplan–Meier curves depicting overall and disease-free survival of patients with colorectal liver metastases, stratified by the new cut-off for histopathological growth patterns categorisation (a–d) and by the predominant growth pattern (e, f). N = 1931 patients with resected colorectal liver metastases.

Fig. 3. H&E image of the escape phenotype.

a Low-magnification image with large necrotic areas in the centre of the CRC liver metastasis, remnants of the desmoplastic rim (D) and vital replacement-type outgrowth at the tumour–liver interface (arrows). This is a ‘halo’ of vital cancer infiltrating the liver tissue for several millimetres at the periphery of the metastasis, with signs of response in its centre. b Higher magnification of the ‘escape’ area with replacement HGP. Li liver, Me metastatic tumour tissue.

Fig. 4. Immunohistochemical staining as an aid to HGP scoring.

a Detection of the replacement HGP in the presence of an extensive immune cell infiltrate that obscures the tumour–liver interface by identification of cancer cell-hepatocyte contact (green arrowheads) at the tumour–liver interface and co-option of hepatocytes (blue arrowheads) in liver lobules undergoing replacement by cancer cells. CK19 (DAB, brown) stains colorectal cancer cells. CK18 (AP, red) stains hepatocytes. Left: low magnification; right: high magnification. b Detection of the pushing-type replacement (type 2) HGP in which the hepatocyte plates are slender (yellow dotted area) and arranged in parallel with the tumour–liver interface. Green arrowheads indicate cancer cell-hepatocyte contact and blue arrowheads hepatocyte co-option. CK19 (DAB, brown) stains colorectal cancer cells. CK18 (AP, red) stains hepatocytes. c Prominent ductular reaction at the tumour–liver interface in the desmoplastic HGP. Areas of ductular reaction (green arrowheads) are present in the outer region of the fibrous rim (green dotted region). Cancer cells are (blue arrow) identified in the metastasis centre, adjacent to necrotic areas (orange star). Right: Detail of the ductular reaction at the tumour–liver interface. Cholangiocytes (CK7 + ) form irregular, angulated, anastomosing ductuli. Note the presence of interspersed cancer cells (CK20 + , blue arrows) within the ductuli, forming common ductular structures. CK20 (DAB, brown) stains colorectal cancer cells. CK7 (AP, red) stains cholangiocytes. d Detection of intrabiliary tumour growth. A discontinuous lining of biliary epithelial cells (blue arrows) can be identified surrounding colorectal cancer cells (sparsely positive for CK20 in this case) with focal contact between colorectal cancer cells and biliary epithelial cells (green stars). CK20 (DAB, brown) stains colorectal cancer cells. CK7 (AP, red) stains cholangiocytes. Left: low magnification; right: high magnification.

Fig. 5. Patient-derived xenograft (PDX) mice models for CRC liver metastases with a desmoplastic and a replacement HGP (H&E images).

a Resected liver metastasis with a desmoplastic HGP (left) and corresponding xenograft PDX model (right). Green arrows indicate the desmoplastic rim in the patient sample and in the liver metastasis of the mouse (PDX#35, see supplementary table 2 in ref. [16]). b Resected liver metastasis with a replacement HGP (left) and corresponding xenograft PDX model (Right). Green arrows indicate some of the areas in which the cancer cells grow into the liver cell plates and contact the hepatocytes, both in the patient sample and in the liver metastasis of the mouse (PDX#30, see supplementary table 2 in ref. [16]).

Fig. 6. Images of melan-A immunostaining of melanoma liver metastases.

a High-magnification images of the tumour–liver interface of a melanoma liver metastasis with a replacement HGP. Small groups of melanoma cells and individual melanoma cells have migrated away from the tumour–liver interface (arrows). b High-magnification images of the tumour–liver interface of a melanoma liver metastasis with a desmoplastic HGP. No migration of melanoma cells in the desmoplastic rim, marked by ‘D’.

Fig. 7. New biological insights into growth patterns through immunohistochemical analyses.

a Remnants of portal zones in the centre of colorectal liver metastases. Left: Detail of a tumour centre in metastasis with a predominant replacement HGP showing remnant of a portal zone with bile duct (green arrowhead) and hepatic artery branch (blue arrowhead). Note colonisation by viable cancer cells of the periportal limiting plate region (orange arrowhead). Caldesmon (DAB, brown) stains smooth muscle cells, mainly in the media layer of the hepatic artery. CK7 (DAB, brown) stains bile duct epithelium. CD34 (AP, red) stains the endothelium of the hepatic artery and of the stromal capillary network. Right: Tumour centre in metastasis with a desmoplastic HGP showing multiple remnants of portal zones between lobules that have undergone complete replacement by cancer cells (orange arrowheads). The bile ducts (green arrows) and branches of the hepatic artery (blue arrows) are embedded in NGFR + portal stroma (yellow arrowheads). CD146 (DAB, brown) stains smooth muscle cells (mainly in the wall of hepatic arteries) and areas of ductular reaction. NGFR (AP, red) stains activated portal fibroblasts and stellate cells. b Intrabiliary tumour growth in a CRC liver metastasis. Left: Densely packed cancer cells (green stars) show exophytic growth and fill the bile duct lumen. Portions of the preserved biliary epithelium (blue arrows) are still identified. Right: Detail illustrating the replacement-like growth of cancer cells, which progress by establishing direct contact with and replacing the cholangiocytes while co-opting their basal membrane. CK20 (DAB, brown) stains colorectal cancer cells. CK7 (AP, red) stains cholangiocytes. c Hybrid cancer cell–cholangiocyte ductular structures. Ductular reaction in the desmoplastic rim with cancer cells (CK20-positive, DAB, brown) forming hybrid structures with cholangiocytes (CK7-positive, AP, red). d Stromal cell heterogeneity in metastasis with a desmoplastic HGP. Top. The outer region of the desmoplastic rim stains strongly positively for NGFR (left, green arrows) and α-smooth muscle actin (alpha-SMA) (Right, green arrowheads), consistent with activated portal/stellate cell stroma. In contrast, the stroma in the metastasis centre is positive for alpha-SMA but negative for NGFR, indicating a desmoplastic character (left and right, blue arrows). Bottom. Reference illustrations of activated portal stroma in the non-neoplastic liver, showing (left) NGFR and (right) alpha-SMA immunoreactivity (left and right, green arrows). CD146 (DAB, brown) stains vascular and sinusoidal endothelium and smooth muscle in branches of the hepatic artery and portal vein. NGFR (AP, red) stains activated portal fibroblasts and stellate cells. CK18 (DAB, brown) stains hepatocytes and cholangiocytes. Alpha-SMA (AP, red) stains activated portal fibroblasts, stellate cells and desmoplasia-associated myofibroblasts. e Ductular reaction in the desmoplastic rim with cells with a hepatocyte-like (CK18-positive, AP, red) and a cholangiocytes-like (CK18, DAB, brown) phenotype (green arrows).