Can plants get cancer? - pathology

What the plant tumor example actually shows

The one supplied paper that deals with a plant growth resembling a tumor describes clubroot, a disease of cruciferous plants such as rapeseed caused by the pathogen Plasmodiophora brassicae [4]. The researchers call it a tumor-formation root pathogen, and their interest was agricultural: they wanted to see whether nitrogen-fixing rhizobia could get into non-leguminous crops by piggybacking on the infection. Rhizobia were found inside infected rapeseed roots in the field, and under laboratory conditions the bacterium Mesorhizobium huakuii could colonize the roots and even fix nitrogen in infected plants [4].

That is a story about a pathogen-induced swelling and about a clever route into plant tissue, not a demonstration that plants spontaneously develop cancer. The paper reports that the rhizobium eased clubroot symptoms and promoted growth of diseased rapeseed, and that early symbiosis-related genes were switched on in Arabidopsis during infection [4]. None of this tells us whether plant cells acquire the unchecked, spreading behavior that defines cancer in animals.

Why the animal cancer papers cannot answer the plant question

Several supplied papers are about cancer in animals or human tissue, and they are useful mainly for showing how differently the question is framed outside botany. One synthesizes evidence that cancer is exceptionally rare in turtles despite their long lives and large bodies, and suggests that high resistance to oxidative stress and protein dysregulation may contribute to that resistance [2]. Another describes a deep-learning method for spotting breast cancer metastases in gigapixel pathology images, where the task is finding tumor tissue that has spread away from the breast [3]. A third reviews how cytokines, small molecular messengers, regulate both pro- and antitumor processes such as inflammation, blood-vessel growth, invasion, and metastasis [5].

Each of these is a study of animal or human disease pathology. None of them examines a plant developing cancer, so they cannot be used to claim that plants do or do not get cancer. They do, however, illustrate the features researchers look for in animal cancer, such as metastasis and immune signaling, which are the kind of features the plant literature supplied here does not test.

A plant extract tested on human cancer cells is not plant cancer

One paper can easily be misread as plant cancer research because it involves blueberry plants. In fact, it tested leaf extracts from blueberry plants, some treated with methyl jasmonate, for their ability to slow the growth and invasion of human gastric cancer cells in the laboratory [1]. The plants were the source of the extract; the cancer was human. The paper's own framing treats gastric cancer as a human health problem with high tumor incidence and mortality [1].

So this study belongs with the animal and human cancer papers, not with the clubroot example. It tells us that plant compounds can be screened against human tumor cells, but it says nothing about whether a blueberry plant, or any plant, can develop cancer itself.

What would count as plant cancer, and what the evidence leaves open

The supplied papers do not settle the broader biological question. The clubroot work shows that a plant pathogen can drive tumor-like root growth and that this growth can be exploited for nitrogen fixation [4], but it does not describe plant cells breaking free and spreading through the plant body the way metastases spread in the breast cancer imaging study [3]. The cytokine review describes signaling that shapes tumor development in animals [5], and the turtle paper describes natural cancer resistance in an animal [2]; neither examines equivalent processes in plants.

For a general reader, the honest answer is therefore narrow. Plants can grow abnormal, tumor-like swellings, and pathogens can trigger them, as clubroot does in rapeseed [4]. Whether those growths should be called cancer, and whether plants have their own cancer-like diseases beyond the examples studied here, is not answered by the supplied evidence.

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